Compare commits

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25 Commits

Author SHA1 Message Date
Russ Cox
7998d012b9 [release-branch.r57] docs/GoCourseDay1.pdf: fix error in operator table.
««« CL 4637041 / df607ef238c9
docs/GoCourseDay1.pdf: fix error in operator table.
Communications op was listed as a binary; it isn't any more.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4637041
»»»

R=r
CC=golang-dev
https://golang.org/cl/4634042
2011-06-16 02:04:56 -04:00
Russ Cox
891ffb6aea [release-branch.r57] docs: Update notes for 3-day Go course.
««« CL 4605041 / 71776ebc7416
docs: Update notes for 3-day Go course.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4605041
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4635041
2011-06-16 01:57:02 -04:00
Russ Cox
cb8903a64d [release-branch.r57] doc: document r57.2
««« CL 4627042 / 9fadba82ab03
doc: document r57.2

R=adg, r
CC=golang-dev
https://golang.org/cl/4627042
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4633041
2011-06-16 01:50:35 -04:00
Russ Cox
0587bf5294 [release-branch.r57] 6g, 8g: fix goto fix
««« CL 4632041 / cbc2b570b2ca
6g, 8g: fix goto fix

R=ken2
CC=golang-dev
https://golang.org/cl/4632041
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4631042
2011-06-16 01:35:30 -04:00
Russ Cox
60b63d2410 [release-branch.r57] gc: work around goto bug
««« CL 4629042 / ec3b60d1fe6e
gc: work around goto bug

R=ken2
CC=golang-dev
https://golang.org/cl/4629042
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4631041
2011-06-16 01:04:43 -04:00
Rob Pike
c57f672d63 reflect: make allocation test less fragile.
When GOMAXPROCS>1, the testing framework runs in parallel with the
test itself and may do a small number of allocations, so allow the
"noAllocs" condition to admit just a few.

Fixes #1782.

R=rsc
CC=golang-dev
https://golang.org/cl/4533041
2011-05-08 08:32:18 -07:00
Russ Cox
16b4a007de [release-branch.r57] doc: document r57.1
««« CL 4471041 / 8339a04966bb
doc: document r57.1

R=adg
CC=golang-dev
https://golang.org/cl/4471041
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4468042
2011-05-04 00:17:17 -04:00
Russ Cox
0bd41f1e48 [release-branch.r57] http: fix FormFile nil pointer dereference on missing multipart form
««« CL 4463042 / 6294ca33c042
http: fix FormFile nil pointer dereference on missing  multipart form

R=rsc
CC=golang-dev
https://golang.org/cl/4463042
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4467042
2011-05-03 23:53:31 -04:00
Russ Cox
ca2cb382ba [release-branch.r57] doc: release.r57
««« CL 4457049 / d222384d1bad
doc: release.r57

R=golang-dev, r, adg, r2
CC=golang-dev
https://golang.org/cl/4457049
»»»

R=golang-dev
TBR=r
CC=golang-dev
https://golang.org/cl/4431087
2011-05-03 14:07:31 -04:00
Russ Cox
658a82a13b [release-branch.r57] Make.cmd: create TARGDIR if necessary
««« CL 4437089 / b2670a39da7c
Make.cmd: create TARGDIR if necessary

Fixes #1771.

R=adg, rsc1
CC=golang-dev
https://golang.org/cl/4437089
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4454054
2011-05-03 12:53:51 -04:00
Russ Cox
9f89972666 [release-branch.r57] reflect: allow unexported key in Value.MapIndex
««« CL 4444087 / 9abf81a9df90
reflect: allow unexported key in Value.MapIndex

Fixes #1748.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4444087
»»»

R=r, r2
CC=golang-dev
https://golang.org/cl/4433099
2011-05-03 11:08:57 -04:00
Russ Cox
125e91a174 [release-branch.r57] jpeg: speed up RGBA encoding ~%50
««« CL 4433088 / 099dd59d3976
jpeg: speed up RGBA encoding ~%50

Avoids image.At(), color.RGBA(), opposing 8 bit shifts,
and min function calls in a loop.  Not as pretty as before,
but the pure version is still there to revert back to
later if/when the compiler gets better.

before (best of 5)
jpeg.BenchmarkEncodeRGBOpaque   50   64781360 ns/op   18.97 MB/s

after (best of 5)
jpeg.BenchmarkEncodeRGBOpaque   50   42044300 ns/op   29.23 MB/s

(benchmarked on an HP z600; 16 core Xeon E5520 @ 2.27Ghz)

R=r, r2, nigeltao
CC=golang-dev
https://golang.org/cl/4433088
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4431086
2011-05-03 01:50:43 -04:00
Russ Cox
3854d346f6 [release-branch.r57] doc/install: specify clone -u instead of -r
««« CL 4435081 / 48c0b02c6e7f
doc/install: specify clone -u instead of -r

R=rsc
CC=golang-dev
https://golang.org/cl/4435081
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4436080
2011-05-03 01:46:11 -04:00
Russ Cox
348ffe7786 [release-branch.r57] image: fix build
««« CL 4438090 / 29f6e2e230a3
image: fix build
accidentally deleted one method
TBR=rsc

R=rsc
CC=golang-dev
https://golang.org/cl/4438090
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4445084
2011-05-03 01:45:33 -04:00
Russ Cox
69e88b5c52 [release-branch.r57] image: add type-specific Set methods and use them when decoding PNG.
««« CL 4428080 / 2098f7682f2d
image: add type-specific Set methods and use them when decoding PNG.
This speeds up PNG decode about 20% by avoiding per-pixel interface conversions.

R=nigeltao, rsc
CC=golang-dev
https://golang.org/cl/4428080
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4426078
2011-05-03 01:45:01 -04:00
Russ Cox
006e5e279b [release-branch.r57] http/pprof: fix POST reading bug
««« CL 4430075 / ca45c67d28cf
http/pprof: fix POST reading bug

R=bradfitz
CC=golang-dev
https://golang.org/cl/4430075
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4454053
2011-05-03 01:43:30 -04:00
Russ Cox
5af3c75e30 [release-branch.r57] 5a, 6a, 8a, cc: remove old environment variables
««« CL 4445079 / f8cc81f985e5
5a, 6a, 8a, cc: remove old environment variables

Uses of $INCLUDE and $NPROC are left over from Plan 9.
Remove them to avoid causing confusion.

R=golang-dev, r2
CC=golang-dev
https://golang.org/cl/4445079
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4438096
2011-05-03 01:42:19 -04:00
Russ Cox
a7ae73d4e0 [release-branch.r57] runtime, sync/atomic: fix arm cas
««« CL 4436072 / e280d98747be
runtime, sync/atomic: fix arm cas

Works around bug in kernel implementation on old ARM5 kernels.
Bug was fixed on 26 Nov 2007 (between 2.6.23 and 2.6.24) but
old kernels persist.

Fixes #1750.

R=dfc, golang-dev
CC=golang-dev
https://golang.org/cl/4436072
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4452064
2011-05-03 01:41:28 -04:00
Russ Cox
6a9e2c7279 [release-branch.r57] png: speed up opaque RGBA encoding
««« CL 4432077 / 66eb68cbd5c2
png: speed up opaque RGBA encoding

With Linux/8g on a 2006 Mac Mini (1.66 GHz Intel Core Duo,
2KB L1, 2MB L2, 2G main memory), GOMAXPROCS unset:

start:
png.BenchmarkEncodePaletted	      50	  44772820 ns/op
png.BenchmarkEncodeRGBOpaque	      10	 208395900 ns/op
png.BenchmarkEncodeRGBA		       5	 331088000 ns/op

remove interface method calls:
png.BenchmarkEncodePaletted	      50	  44722880 ns/op
png.BenchmarkEncodeRGBOpaque	      10	 139042600 ns/op
png.BenchmarkEncodeRGBA		       5	 334033600 ns/op

flate inline min/max():
png.BenchmarkEncodePaletted	      50	  40631180 ns/op
png.BenchmarkEncodeRGBOpaque	      10	 124894900 ns/op
png.BenchmarkEncodeRGBA		       5	 312099000 ns/op

after adler change:
png.BenchmarkEncodePaletted	      50	  40181760 ns/op
png.BenchmarkEncodeRGBOpaque	      20	 121781950 ns/op
png.BenchmarkEncodeRGBA		       5	 313890800 ns/op

In comparison to 121 ms on this 2006 machine, on my
Core2 Duo 2.66 GHz laptop, the final BenchmarkEncodeRGBOpaque
runs in 27 ms. (these are all for 640x480 images)

R=nigeltao, rsc, r
CC=golang-dev
https://golang.org/cl/4432077
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4430076
2011-05-03 01:40:19 -04:00
Russ Cox
50e57603ab [release-branch.r57] http: rename ErrBodyReadAferClose to ErrBodyReadAfterClose
««« CL 4432085 / 370c77323b75
http: rename ErrBodyReadAferClose to ErrBodyReadAfterClose

R=bradfitz, dsymonds
CC=golang-dev
https://golang.org/cl/4432085
»»»

TBR=adg
CC=golang-dev
https://golang.org/cl/4425086
2011-05-03 01:39:17 -04:00
Russ Cox
d00421a6b1 [release-branch.r57] mime/multipart: fix regression from previous ReadSlice change
««« CL 4432083 / 698b5ea9c782
mime/multipart: fix regression from previous ReadSlice change

The previous change to make multipart use ReadSlice out of
paranoia broke multipart to not deal with large lines in
the bodies.

We should only be paranoid about long lines in the header
sections.

Fixes http://code.google.com/p/camlistore/issues/detail?id=4

R=adg
CC=golang-dev
https://golang.org/cl/4432083
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4452062
2011-05-03 01:15:56 -04:00
Russ Cox
b69a320781 [release-branch.r57] http: new error for reading a body after it's been closed
««« CL 4433094 / e30213b07276
http: new error for reading a body after it's been closed

R=adg
CC=golang-dev
https://golang.org/cl/4433094
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4433098
2011-05-03 01:15:41 -04:00
Russ Cox
ed54b19716 [release-branch.r57] image: png & jpeg encoding benchmarks
««« CL 4445074 / 304d7d2b1d6c
image: png & jpeg encoding benchmarks

No code changes in this CL.

R=r
CC=golang-dev
https://golang.org/cl/4445074
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4453056
2011-05-03 01:15:26 -04:00
Russ Cox
29fdaadbef [release-branch.r57] xml: fix reflect error
««« CL 4431075 / acee6ec98e9a
xml: fix reflect error

Fixes #1749.

R=bradfitz
CC=golang-dev
https://golang.org/cl/4431075
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4457048
2011-05-03 01:15:12 -04:00
Russ Cox
5ce9a8d4fc create release-branch.r57 2011-05-03 01:07:23 -04:00
3510 changed files with 131361 additions and 340678 deletions

View File

@@ -3,7 +3,7 @@ syntax:glob
.git
.gitignore
*.[568ao]
*.a[568o]
*.ao
*.so
*.pyc
._*
@@ -23,31 +23,33 @@ _test
_testmain.go
build.out
test.out
doc/tmpltohtml
doc/articles/wiki/*.bin
y.tab.[ch]
doc/htmlgen
doc/codelab/wiki/*.bin
misc/cgo/life/run.out
misc/cgo/stdio/run.out
misc/cgo/testso/main
misc/dashboard/builder/builder
misc/dashboard/builder/gobuilder
misc/goplay/goplay
misc/osx/*.pkg
misc/osx/*.dmg
src/Make.inc
src/cmd/6a/6a
src/cmd/?a/y.output
src/cmd/?l/enam.c
src/cmd/cc/y.output
src/cmd/dist/dist.dSYM
src/cmd/gc/builtin.c
src/cmd/gc/mkbuiltin1
src/cmd/gc/opnames.h
src/cmd/gc/y.output
src/pkg/exp/norm/maketables
src/pkg/exp/norm/maketesttables
src/pkg/exp/norm/normregtest
src/pkg/exp/ebnflint/ebnflint
src/pkg/go/doc/headscan
src/cmd/gc/y1.tab.c
src/cmd/gc/yerr.h
src/cmd/goinstall/syslist.go
src/pkg/Make.deps
src/pkg/exp/ogle/ogle
src/pkg/os/signal/unix.go
src/pkg/runtime/*/asm.h
src/pkg/runtime/goc2c
src/pkg/runtime/mkversion
src/pkg/runtime/z*
src/pkg/runtime/runtime.acid.*
src/pkg/runtime/runtime_defs.go
src/pkg/runtime/version.go
src/pkg/runtime/version_*.go
src/pkg/unicode/maketables
src/pkg/*.*/
test/pass.out
@@ -55,8 +57,6 @@ test/run.out
test/times.out
test/garbage/*.out
goinstall.log
last-change
VERSION.cache
syntax:regexp
^bin/

50
.hgtags
View File

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68
AUTHORS
View File

@@ -11,15 +11,10 @@
Abhinav Gupta <abhinav.g90@gmail.com>
Adrian O'Grady <elpollouk@gmail.com>
Albert Strasheim <fullung@gmail.com>
Aleksandar Dezelin <dezelin@gmail.com>
Alex Brainman <alex.brainman@gmail.com>
Alexander Orlov <alexander.orlov@loxal.net>
Alexander Reece <awreece@gmail.com>
Alexey Borzenkov <snaury@gmail.com>
Amrut Joshi <amrut.joshi@gmail.com>
Andrei Vieru <euvieru@gmail.com>
Andrew Balholm <andybalholm@gmail.com>
Andrew Pritchard <awpritchard@gmail.com>
Andrew Skiba <skibaa@gmail.com>
Andrey Mirtchovski <mirtchovski@gmail.com>
Andy Davis <andy@bigandian.com>
@@ -31,132 +26,85 @@ Aron Nopanen <aron.nopanen@gmail.com>
Arvindh Rajesh Tamilmani <art@a-30.net>
Ben Olive <sionide21@gmail.com>
Benny Siegert <bsiegert@gmail.com>
Berengar Lehr <berengar.lehr@gmx.de>
Bjorn Tipling <bjorn.tipling@gmail.com>
Blake Mizerany <blake.mizerany@gmail.com>
Bobby Powers <bobbypowers@gmail.com>
Caine Tighe <arctanofyourface@gmail.com>
Charles L. Dorian <cldorian@gmail.com>
Chris Dollin <ehog.hedge@gmail.com>
Chris Farmiloe <chrisfarms@gmail.com>
Chris Jones <chris@cjones.org>
Chris Lennert <calennert@gmail.com>
Christian Himpel <chressie@googlemail.com>
Christoph Hack <christoph@tux21b.org>
Christopher Nielsen <m4dh4tt3r@gmail.com>
Christopher Redden <christopher.redden@gmail.com>
Christopher Wedgwood <cw@f00f.org>
Clement Skau <clementskau@gmail.com>
Conrad Meyer <cemeyer@cs.washington.edu>
Corey Thomasson <cthom.lists@gmail.com>
Damian Gryski <dgryski@gmail.com>
Dan Sinclair <dan.sinclair@gmail.com>
Daniel Fleischman <danielfleischman@gmail.com>
Daniel Krech <eikeon@eikeon.com>
Daniel Theophanes <kardianos@gmail.com>
Darren Elwood <darren@textnode.com>
Dave Cheney <dave@cheney.net>
David du Colombier <0intro@gmail.com>
David Forsythe <dforsythe@gmail.com>
David G. Andersen <dave.andersen@gmail.com>
David Jakob Fritz <david.jakob.fritz@gmail.com>
David Titarenco <david.titarenco@gmail.com>
Dean Prichard <dean.prichard@gmail.com>
Devon H. O'Dell <devon.odell@gmail.com>
Dmitry Chestnykh <dchest@gmail.com>
Eden Li <eden.li@gmail.com>
Eivind Uggedal <eivind@uggedal.com>
Emil Hessman <c.emil.hessman@gmail.com>
Eoghan Sherry <ejsherry@gmail.com>
Eric Clark <zerohp@gmail.com>
Eric Eisner <eric.d.eisner@gmail.com>
Esko Luontola <esko.luontola@gmail.com>
Evan Shaw <chickencha@gmail.com>
Fan Hongjian <fan.howard@gmail.com>
Fazlul Shahriar <fshahriar@gmail.com>
Firmansyah Adiputra <frm.adiputra@gmail.com>
Florian Uekermann <florian@uekermann-online.de>
Florian Weimer <fw@deneb.enyo.de>
Francisco Souza <franciscossouza@gmail.com>
Gary Burd <gary@beagledreams.com>
Gideon Jan-Wessel Redelinghuys <gjredelinghuys@gmail.com>
Giles Lean <giles.lean@pobox.com>
Google Inc.
Graham Miller <graham.miller@gmail.com>
Gustav Paul <gustav.paul@gmail.com>
Gustavo Niemeyer <gustavo@niemeyer.net>
Gwenael Treguier <gwenn.kahz@gmail.com>
Harley Laue <losinggeneration@gmail.com>
Hector Chu <hectorchu@gmail.com>
Hong Ruiqi <hongruiqi@gmail.com>
Icarus Sparry <golang@icarus.freeuk.com>
Ingo Oeser <nightlyone@googlemail.com>
Isaac Wagner <ibw@isaacwagner.me>
James Fysh <james.fysh@gmail.com>
James Meneghello <rawrz0r@gmail.com>
James P. Cooper <jamespcooper@gmail.com>
James Toy <nil@opensesame.st>
James Whitehead <jnwhiteh@gmail.com>
Jan H. Hosang <jan.hosang@gmail.com>
Jan Mercl <befelemepeseveze@gmail.com>
Jan Newmarch <jan.newmarch@gmail.com>
Jani Monoses <jani.monoses@ubuntu.com>
Jaroslavas Počepko <jp@webmaster.ms>
Jeff Hodges <jeff@somethingsimilar.com>
Jeff R. Allen <jra@nella.org>
Jeremy Jackins <jeremyjackins@gmail.com>
Jim McGrath <jimmc2@gmail.com>
Joe Poirier <jdpoirier@gmail.com>
John Asmuth <jasmuth@gmail.com>
Jonathan Mark <jhmark@xenops.com>
Jonathan Wills <runningwild@gmail.com>
Jongmin Kim <atomaths@gmail.com>
Jose Luis Vázquez González <josvazg@gmail.com>
Josh Goebel <dreamer3@gmail.com>
Jukka-Pekka Kekkonen <karatepekka@gmail.com>
Julian Phillips <julian@quantumfyre.co.uk>
Kai Backman <kaib@golang.org>
Kei Son <hey.calmdown@gmail.com>
Keith Rarick <kr@xph.us>
Ken Friedenbach <kenliz@cruzio.com>
Ken Rockot <ken@oz.gs>
Kevin Ballard <kevin@sb.org>
Kyle Consalus <consalus@gmail.com>
Kyle Lemons <kyle@kylelemons.net>
Lai Jiangshan <eag0628@gmail.com>
Lorenzo Stoakes <lstoakes@gmail.com>
Luca Greco <luca.greco@alcacoop.it>
Lucio De Re <lucio.dere@gmail.com>
Luit van Drongelen <luitvd@gmail.com>
Markus Duft <markus.duft@salomon.at>
Martin Neubauer <m.ne@gmx.net>
Mateusz Czapliński <czapkofan@gmail.com>
Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
Matthew Horsnell <matthew.horsnell@gmail.com>
Micah Stetson <micah.stetson@gmail.com>
Michael Elkins <michael.elkins@gmail.com>
Michael Hoisie <hoisie@gmail.com>
Michał Derkacz <ziutek@lnet.pl>
Miek Gieben <miek@miek.nl>
Mikael Tillenius <mikti42@gmail.com>
Mike Rosset <mike.rosset@gmail.com>
Miki Tebeka <miki.tebeka@gmail.com>
Mikio Hara <mikioh.mikioh@gmail.com>
Mikkel Krautz <mikkel@krautz.dk>
Moriyoshi Koizumi <mozo@mozo.jp>
Môshe van der Sterre <moshevds@gmail.com>
ngmoco, LLC
Nicholas Waples <nwaples@gmail.com>
Nigel Kerr <nigel.kerr@gmail.com>
Olivier Antoine <olivier.antoine@gmail.com>
Olivier Duperray <duperray.olivier@gmail.com>
Padraig Kitterick <padraigkitterick@gmail.com>
Paolo Giarrusso <p.giarrusso@gmail.com>
Pascal S. de Kloe <pascal@quies.net>
Patrick Gavlin <pgavlin@gmail.com>
Patrick Mylund Nielsen <patrick@patrickmn.com>
Paul Lalonde <paul.a.lalonde@gmail.com>
Paul Sbarra <Sbarra.Paul@gmail.com>
Petar Maymounkov <petarm@gmail.com>
Peter Froehlich <peter.hans.froehlich@gmail.com>
Peter Mundy <go.peter.90@gmail.com>
@@ -164,44 +112,30 @@ Peter Williams <pwil3058@gmail.com>
Pieter Droogendijk <pieter@binky.org.uk>
Quan Yong Zhai <qyzhai@gmail.com>
Raif S. Naffah <go@naffah-raif.name>
Rémy Oudompheng <oudomphe@phare.normalesup.org>
Risto Jaakko Saarelma <rsaarelm@gmail.com>
Robert Figueiredo <robfig@gmail.com>
Robert Hencke <robert.hencke@gmail.com>
Roger Pau Monné <royger@gmail.com>
Roger Peppe <rogpeppe@gmail.com>
Ron Minnich <rminnich@gmail.com>
Ross Light <rlight2@gmail.com>
Ryan Hitchman <hitchmanr@gmail.com>
Sanjay Menakuru <balasanjay@gmail.com>
Scott Lawrence <bytbox@gmail.com>
Sebastien Binet <seb.binet@gmail.com>
Sébastien Paolacci <sebastien.paolacci@gmail.com>
Sergei Skorobogatov <skorobo@rambler.ru>
Sergey 'SnakE' Gromov <snake.scaly@gmail.com>
Sergio Luis O. B. Correia <sergio@larces.uece.br>
Shenghou Ma <minux.ma@gmail.com>
Spring Mc <heresy.mc@gmail.com>
Stefan Nilsson <snilsson@nada.kth.se> <trolleriprofessorn@gmail.com>
Stefan Nilsson <snilsson@nada.kth.se>
Stephen Weinberg <stephen@q5comm.com>
Sven Almgren <sven@tras.se>
Szabolcs Nagy <nsz@port70.net>
Tarmigan Casebolt <tarmigan@gmail.com>
Taru Karttunen <taruti@taruti.net>
Timo Savola <timo.savola@gmail.com>
Tor Andersson <tor.andersson@gmail.com>
Ugorji Nwoke <ugorji@gmail.com>
Vadim Vygonets <unixdj@gmail.com>
Vincent Ambo <tazjin@googlemail.com>
Vincent Vanackere <vincent.vanackere@gmail.com>
Vinu Rajashekhar <vinutheraj@gmail.com>
Volker Dobler <dr.volker.dobler@gmail.com>
Wei Guangjing <vcc.163@gmail.com>
William Josephson <wjosephson@gmail.com>
Yasuhiro Matsumoto <mattn.jp@gmail.com>
Yissakhar Z. Beck <yissakhar.beck@gmail.com>
Yongjian Xu <i3dmaster@gmail.com>
Yoshiyuki Kanno <nekotaroh@gmail.com> <yoshiyuki.kanno@stoic.co.jp>
Yuusei Kuwana <kuwana@kumama.org>
Yuval Pavel Zholkover <paulzhol@gmail.com>
Ziad Hatahet <hatahet@gmail.com>

View File

@@ -35,18 +35,11 @@ Abhinav Gupta <abhinav.g90@gmail.com>
Adam Langley <agl@golang.org>
Adrian O'Grady <elpollouk@gmail.com>
Albert Strasheim <fullung@gmail.com>
Aleksandar Dezelin <dezelin@gmail.com>
Alex Brainman <alex.brainman@gmail.com>
Alexander Orlov <alexander.orlov@loxal.net>
Alexander Reece <awreece@gmail.com>
Alexandru Moșoi <brtzsnr@gmail.com>
Alexey Borzenkov <snaury@gmail.com>
Amrut Joshi <amrut.joshi@gmail.com>
Andrea Spadaccini <spadaccio@google.com>
Andrei Vieru <euvieru@gmail.com>
Andrew Balholm <andybalholm@gmail.com>
Andrew Gerrand <adg@golang.org>
Andrew Pritchard <awpritchard@gmail.com>
Andrew Skiba <skibaa@gmail.com>
Andrey Mirtchovski <mirtchovski@gmail.com>
Andy Davis <andy@bigandian.com>
@@ -59,48 +52,34 @@ Arvindh Rajesh Tamilmani <art@a-30.net>
Austin Clements <aclements@csail.mit.edu>
Balazs Lecz <leczb@google.com>
Ben Eitzen <eitzenb@golang.org>
Ben Fried <ben.fried@gmail.com>
Ben Lynn <benlynn@gmail.com>
Ben Olive <sionide21@gmail.com>
Benny Siegert <bsiegert@gmail.com>
Berengar Lehr <Berengar.Lehr@gmx.de>
Bill Neubauer <wcn@golang.org> <wcn@google.com>
Bjorn Tipling <bjorn.tipling@gmail.com>
Blake Mizerany <blake.mizerany@gmail.com>
Bobby Powers <bobbypowers@gmail.com>
Brad Fitzpatrick <bradfitz@golang.org> <bradfitz@gmail.com>
Brendan O'Dea <bod@golang.org>
Caine Tighe <arctanofyourface@gmail.com>
Cary Hull <chull@google.com>
Charles L. Dorian <cldorian@gmail.com>
Chris Dollin <ehog.hedge@gmail.com>
Chris Farmiloe <chrisfarms@gmail.com>
Chris Hundt <hundt@google.com>
Chris Jones <chris@cjones.org> <chris.jones.yar@gmail.com>
Chris Lennert <calennert@gmail.com>
Christian Himpel <chressie@googlemail.com> <chressie@gmail.com>
Christoph Hack <christoph@tux21b.org>
Christopher Nielsen <m4dh4tt3r@gmail.com>
Christopher Redden <christopher.redden@gmail.com>
Christopher Wedgwood <cw@f00f.org>
Clement Skau <clementskau@gmail.com>
Conrad Meyer <cemeyer@cs.washington.edu>
Corey Thomasson <cthom.lists@gmail.com>
Damian Gryski <dgryski@gmail.com>
Dan Sinclair <dan.sinclair@gmail.com>
Daniel Fleischman <danielfleischman@gmail.com>
Daniel Krech <eikeon@eikeon.com>
Daniel Nadasi <dnadasi@google.com>
Daniel Theophanes <kardianos@gmail.com>
Darren Elwood <darren@textnode.com>
Dave Cheney <dave@cheney.net>
Dave Grijalva <dgrijalva@ngmoco.com>
David Anderson <danderson@google.com>
David Crawshaw <david.crawshaw@zentus.com> <crawshaw@google.com>
David du Colombier <0intro@gmail.com>
David Crawshaw <david.crawshaw@zentus.com>
David Forsythe <dforsythe@gmail.com>
David G. Andersen <dave.andersen@gmail.com>
David Jakob Fritz <david.jakob.fritz@gmail.com>
David Symonds <dsymonds@golang.org>
David Titarenco <david.titarenco@gmail.com>
Dean Prichard <dean.prichard@gmail.com>
@@ -108,109 +87,66 @@ Devon H. O'Dell <devon.odell@gmail.com>
Dmitriy Vyukov <dvyukov@google.com>
Dmitry Chestnykh <dchest@gmail.com>
Eden Li <eden.li@gmail.com>
Eivind Uggedal <eivind@uggedal.com>
Emil Hessman <c.emil.hessman@gmail.com>
Eoghan Sherry <ejsherry@gmail.com>
Eric Clark <zerohp@gmail.com>
Eric Eisner <eric.d.eisner@gmail.com>
Esko Luontola <esko.luontola@gmail.com>
Evan Martin <evan.martin@gmail.com>
Evan Shaw <chickencha@gmail.com>
Fan Hongjian <fan.howard@gmail.com>
Fazlul Shahriar <fshahriar@gmail.com>
Firmansyah Adiputra <frm.adiputra@gmail.com>
Florian Uekermann <florian@uekermann-online.de> <f1@uekermann-online.de>
Florian Weimer <fw@deneb.enyo.de>
Francisco Souza <franciscossouza@gmail.com>
Fumitoshi Ukai <ukai@google.com>
Gary Burd <gary@beagledreams.com> <gary.burd@gmail.com>
Gideon Jan-Wessel Redelinghuys <gjredelinghuys@gmail.com>
Giles Lean <giles.lean@pobox.com>
Graham Miller <graham.miller@gmail.com>
Gustav Paul <gustav.paul@gmail.com>
Gustavo Niemeyer <gustavo@niemeyer.net> <n13m3y3r@gmail.com>
Gwenael Treguier <gwenn.kahz@gmail.com>
Harley Laue <losinggeneration@gmail.com>
Hector Chu <hectorchu@gmail.com>
Hong Ruiqi <hongruiqi@gmail.com>
Ian Lance Taylor <iant@golang.org>
Icarus Sparry <golang@icarus.freeuk.com>
Ingo Oeser <nightlyone@googlemail.com> <nightlyone@gmail.com>
Isaac Wagner <ibw@isaacwagner.me>
Ivan Krasin <krasin@golang.org>
Jacob Baskin <jbaskin@google.com>
James Aguilar <jaguilar@google.com>
James Fysh <james.fysh@gmail.com>
James Meneghello <rawrz0r@gmail.com>
James P. Cooper <jamespcooper@gmail.com>
James Toy <nil@opensesame.st>
James Whitehead <jnwhiteh@gmail.com>
Jamie Gennis <jgennis@google.com> <jgennis@gmail.com>
Jamie Gennis <jgennis@google.com>
Jan H. Hosang <jan.hosang@gmail.com>
Jan Mercl <befelemepeseveze@gmail.com>
Jan Newmarch <jan.newmarch@gmail.com>
Jani Monoses <jani.monoses@ubuntu.com> <jani.monoses@gmail.com>
Jaroslavas Počepko <jp@webmaster.ms>
Jeff Hodges <jeff@somethingsimilar.com>
Jeff R. Allen <jra@nella.org> <jeff.allen@gmail.com>
Jeremy Jackins <jeremyjackins@gmail.com>
Jim McGrath <jimmc2@gmail.com>
Joe Poirier <jdpoirier@gmail.com>
Joel Sing <jsing@google.com>
Johan Euphrosine <proppy@google.com>
John Asmuth <jasmuth@gmail.com>
John Beisley <huin@google.com>
John DeNero <denero@google.com>
Jonathan Allie <jonallie@google.com>
Jonathan Mark <jhmark@xenops.com> <jhmark000@gmail.com>
Jonathan Pittman <jmpittman@google.com> <jonathan.mark.pittman@gmail.com>
Jonathan Wills <runningwild@gmail.com>
Jongmin Kim <atomaths@gmail.com>
Jos Visser <josv@google.com>
Jose Luis Vázquez González <josvazg@gmail.com>
Josh Goebel <dreamer3@gmail.com>
Jukka-Pekka Kekkonen <karatepekka@gmail.com>
Julian Phillips <julian@quantumfyre.co.uk>
Kai Backman <kaib@golang.org>
Kei Son <hey.calmdown@gmail.com>
Keith Rarick <kr@xph.us>
Ken Friedenbach <kenliz@cruzio.com>
Ken Rockot <ken@oz.gs> <ken.rockot@gmail.com>
Ken Thompson <ken@golang.org>
Kevin Ballard <kevin@sb.org>
Kirklin McDonald <kirklin.mcdonald@gmail.com>
Kyle Consalus <consalus@gmail.com>
Kyle Lemons <kyle@kylelemons.net> <kevlar@google.com>
Lai Jiangshan <eag0628@gmail.com>
Kyle Lemons <kyle@kylelemons.net> <etherealflaim@gmail.com>
Larry Hosken <lahosken@golang.org>
Lorenzo Stoakes <lstoakes@gmail.com>
Louis Kruger <louisk@google.com>
Luca Greco <luca.greco@alcacoop.it>
Lucio De Re <lucio.dere@gmail.com>
Luit van Drongelen <luitvd@gmail.com>
Luuk van Dijk <lvd@golang.org> <lvd@google.com>
Marcel van Lohuizen <mpvl@golang.org>
Mark Zavislak <zavislak@google.com>
Markus Duft <markus.duft@salomon.at>
Martin Neubauer <m.ne@gmx.net>
Mateusz Czapliński <czapkofan@gmail.com>
Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
Matt Jones <mrjones@google.com>
Matthew Horsnell <matthew.horsnell@gmail.com>
Maxim Pimenov <mpimenov@google.com>
Maxim Ushakov <ushakov@google.com>
Micah Stetson <micah.stetson@gmail.com>
Michael Elkins <michael.elkins@gmail.com>
Michael Hoisie <hoisie@gmail.com>
Michael Shields <mshields@google.com>
Michael T. Jones <mtj@google.com> <michael.jones@gmail.com>
Michał Derkacz <ziutek@lnet.pl>
Miek Gieben <miek@miek.nl> <remigius.gieben@gmail.com>
Mikael Tillenius <mikti42@gmail.com>
Mike Rosset <mike.rosset@gmail.com>
Mike Samuel <mikesamuel@gmail.com>
Mike Solomon <msolo@gmail.com>
Miki Tebeka <miki.tebeka@gmail.com>
Mikio Hara <mikioh.mikioh@gmail.com>
Mikkel Krautz <mikkel@krautz.dk> <krautz@gmail.com>
Moriyoshi Koizumi <mozo@mozo.jp>
@@ -219,15 +155,10 @@ Nicholas Waples <nwaples@gmail.com>
Nigel Kerr <nigel.kerr@gmail.com>
Nigel Tao <nigeltao@golang.org>
Olivier Antoine <olivier.antoine@gmail.com>
Olivier Duperray <duperray.olivier@gmail.com>
Padraig Kitterick <padraigkitterick@gmail.com>
Paolo Giarrusso <p.giarrusso@gmail.com>
Pascal S. de Kloe <pascal@quies.net>
Patrick Gavlin <pgavlin@gmail.com>
Patrick Mylund Nielsen <patrick@patrickmn.com>
Paul Borman <borman@google.com>
Paul Lalonde <paul.a.lalonde@gmail.com>
Paul Sbarra <Sbarra.Paul@gmail.com>
Petar Maymounkov <petarm@gmail.com>
Peter Froehlich <peter.hans.froehlich@gmail.com>
Peter McKenzie <petermck@google.com>
@@ -239,57 +170,41 @@ Pieter Droogendijk <pieter@binky.org.uk>
Quan Yong Zhai <qyzhai@gmail.com>
Raif S. Naffah <go@naffah-raif.name>
Raph Levien <raph@google.com>
Rémy Oudompheng <oudomphe@phare.normalesup.org> <remyoudompheng@gmail.com>
Risto Jaakko Saarelma <rsaarelm@gmail.com>
Rob Pike <r@golang.org>
Robert Figueiredo <robfig@gmail.com>
Robert Griesemer <gri@golang.org>
Robert Hencke <robert.hencke@gmail.com>
Roger Pau Monné <royger@gmail.com>
Roger Peppe <rogpeppe@gmail.com>
Ron Minnich <rminnich@gmail.com>
Ross Light <rlight2@gmail.com>
Russ Cox <rsc@golang.org>
Ryan Hitchman <hitchmanr@gmail.com>
Sam Thorogood <thorogood@google.com> <sam.thorogood@gmail.com>
Sameer Ajmani <sameer@golang.org> <ajmani@gmail.com>
Sanjay Menakuru <balasanjay@gmail.com>
Sameer Ajmani <ajmani@gmail.com>
Scott Lawrence <bytbox@gmail.com>
Scott Schwartz <scotts@golang.org>
Sebastien Binet <seb.binet@gmail.com>
Sébastien Paolacci <sebastien.paolacci@gmail.com>
Sergei Skorobogatov <skorobo@rambler.ru>
Sergey 'SnakE' Gromov <snake.scaly@gmail.com>
Sergio Luis O. B. Correia <sergio@larces.uece.br>
Shenghou Ma <minux.ma@gmail.com>
Spring Mc <heresy.mc@gmail.com>
Stefan Nilsson <snilsson@nada.kth.se> <trolleriprofessorn@gmail.com>
Stefan Nilsson <snilsson@nada.kth.se>
Stephen Ma <stephenm@golang.org>
Stephen Weinberg <stephen@q5comm.com>
Sugu Sougoumarane <ssougou@gmail.com>
Sven Almgren <sven@tras.se>
Szabolcs Nagy <nsz@port70.net>
Tarmigan Casebolt <tarmigan@gmail.com>
Taru Karttunen <taruti@taruti.net>
Timo Savola <timo.savola@gmail.com>
Tom Szymanski <tgs@google.com>
Tor Andersson <tor.andersson@gmail.com>
Trevor Strohman <trevor.strohman@gmail.com>
Ugorji Nwoke <ugorji@gmail.com>
Vadim Vygonets <unixdj@gmail.com>
Vincent Ambo <tazjin@googlemail.com>
Vincent Vanackere <vincent.vanackere@gmail.com>
Vinu Rajashekhar <vinutheraj@gmail.com>
Vish Subramanian <vish@google.com>
Volker Dobler <dr.volker.dobler@gmail.com>
Wei Guangjing <vcc.163@gmail.com>
William Chan <willchan@chromium.org>
William Josephson <wjosephson@gmail.com>
Yasuhiro Matsumoto <mattn.jp@gmail.com>
Yissakhar Z. Beck <yissakhar.beck@gmail.com>
Yongjian Xu <i3dmaster@gmail.com>
Yoshiyuki Kanno <nekotaroh@gmail.com> <yoshiyuki.kanno@stoic.co.jp>
Yuusei Kuwana <kuwana@kumama.org>
Yuval Pavel Zholkover <paulzhol@gmail.com>
Yves Junqueira <yves.junqueira@gmail.com>
Ziad Hatahet <hatahet@gmail.com>

View File

@@ -1,4 +1,4 @@
Copyright (c) 2012 The Go Authors. All rights reserved.
Copyright (c) 2009 The Go Authors. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are

24534
api/go1.txt

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BIN
doc/GoCourseDay1.pdf Normal file

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BIN
doc/GoCourseDay2.pdf Normal file

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@@ -2,26 +2,10 @@
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file.
RAWHTML=\
articles/defer_panic_recover.rawhtml\
articles/error_handling.rawhtml\
articles/slices_usage_and_internals.rawhtml\
articles/laws_of_reflection.rawhtml\
articles/c_go_cgo.rawhtml\
articles/concurrency_patterns.rawhtml\
articles/godoc_documenting_go_code.rawhtml\
articles/gobs_of_data.rawhtml\
articles/json_and_go.rawhtml\
articles/json_rpc_tale_of_interfaces.rawhtml\
articles/image_draw.rawhtml\
articles/image_package.rawhtml\
effective_go.rawhtml\
go1.rawhtml\
include ../src/Make.inc
all: $(RAWHTML)
TARG=htmlgen
GOFILES=\
htmlgen.go\
%.rawhtml: %.html
godoc -url /doc/$< >$@
clean:
rm -f $(RAWHTML)
include ../src/Make.cmd

200
doc/all.css Normal file
View File

@@ -0,0 +1,200 @@
/* General Styles */
body {
font-family: "Bitstream Vera Sans", Verdana, sans-serif;
font-size: 81.25%;
line-height: 1.23em;
padding: 0;
margin: 1.23em;
background: white;
color: black;
}
a {
color: #04a;
text-decoration: none;
}
a:visited {
color: #04a;
}
a:hover {
color: #a40;
text-decoration: underline;
}
a:active {
color: #c00;
}
code, pre {
font-size: 1.2em;
}
pre {
background: #F0F0F0;
padding: 0.5em 1em;
}
/* Top bar */
#container {
width: 100%;
margin: auto;
}
#topnav {
height: 55px;
background: url(/doc/logo.png) no-repeat top left;
}
a#logo-box {
display: block;
height: 55px;
}
h1#title {
display: none;
}
#nav-main {
float: right;
width: 500px;
margin-top: -5px;
text-align: center;
}
#nav-main ul {
padding-left: 0;
margin-left: 0;
margin-bottom: 0.5em;
}
#nav-main li a {
display: inline;
display: inline-block;
padding: .46em .62em .38em .62em;
}
#nav-main li a:link,
#nav-main li a:visited {
color: #000;
}
#nav-main li {
display: inline;
display: inline-block;
background: #e6e6e6 url(/doc/button_background.png) repeat-x;
border: solid 1px #999;
margin-left: -1px;
text-shadow: #fff 0 1px 0;
box-shadow: 0 1px 1px #ccc;
-moz-box-shadow: 0 1px 1px #ccc;
-webkit-box-shadow: 0 1px 1px #ccc;
}
#nav-main li:first-child {
-moz-border-top-left-radius: 4px;
border-top-left-radius: 4px;
-moz-border-bottom-left-radius: 4px;
border-bottom-left-radius: 4px;
}
#nav-main li:last-child {
-moz-border-top-right-radius: 4px;
border-top-right-radius: 4px;
-moz-border-bottom-right-radius: 4px;
border-bottom-right-radius: 4px;
}
#nav-main .quickref {
color: #444;
}
#nav-main .quickref .sep {
color: #999;
}
#search {
width: 120px;
margin-left: 0.5em;
}
#search.inactive {
text-align: center;
color: #444;
}
/* Footer */
#site-info {
position: relative;
text-align: center;
}
#site-info, #site-info a:link, #site-info a:visited {
color: #aaa;
}
/* Content */
#content {
clear: both;
padding: 0;
position: relative;
margin-top: 1.5em;
margin-bottom: 1.5em;
border-top: solid 1px #aaa;
border-bottom: solid 1px #aaa;
}
.left-column {
width: 49%;
float: left;
}
.right-column {
width: 49%;
float: right;
}
.end-columns {
clear: both;
}
#content h1 {
margin-bottom: -0em;
padding: 0;
}
#content h2 {
border-top: 2px solid #ddd;
padding: 8px 5px;
margin: 1.5em 0 0;
}
#content .subtitle {
margin-top: 1em;
display: block;
}
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font-weight: normal; font-size: 7pt;
float: right; color: #999;
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background: #FFFFE0;
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span.ln {
font-size: 80%;
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color: #002090;
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background: #FF9900;
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@@ -1,180 +0,0 @@
<!--{
"Title": "C? Go? Cgo!",
"Template": true
}-->
<p>
Cgo lets Go packages call C code. Given a Go source file written with some
special features, cgo outputs Go and C files that can be combined into a
single Go package.
</p>
<p>
To lead with an example, here's a Go package that provides two functions -
<code>Random</code> and <code>Seed</code> - that wrap C's <code>random</code>
and <code>srandom</code> functions.
</p>
{{code "/doc/progs/cgo1.go" `/package rand/` `/END/`}}
<p>
Let's look at what's happening here, starting with the import statement.
</p>
<p>
The <code>rand</code> package imports <code>"C"</code>, but you'll find there's
no such package in the standard Go library. That's because <code>C</code> is a
"pseudo-package", a special name interpreted by cgo as a reference to C's
name space.
</p>
<p>
The <code>rand</code> package contains four references to the <code>C</code>
package: the calls to <code>C.random</code> and <code>C.srandom</code>, the
conversion <code>C.uint(i)</code>, and the <code>import</code> statement.
</p>
<p>
The <code>Random</code> function calls the standard C library's <code>random</code>
function and returns the result. In C, <code>random</code> returns a value of the
C type <code>long</code>, which cgo represents as the type <code>C.long</code>.
It must be converted to a Go type before it can be used by Go code outside this
package, using an ordinary Go type conversion:
</p>
{{code "/doc/progs/cgo1.go" `/func Random/` `/STOP/`}}
<p>
Here's an equivalent function that uses a temporary variable to illustrate
the type conversion more explicitly:
</p>
{{code "/doc/progs/cgo2.go" `/func Random/` `/STOP/`}}
<p>
The <code>Seed</code> function does the reverse, in a way. It takes a
regular Go <code>int</code>, converts it to the C <code>unsigned int</code>
type, and passes it to the C function <code>srandom</code>.
</p>
{{code "/doc/progs/cgo1.go" `/func Seed/` `/END/`}}
<p>
Note that cgo knows the <code>unsigned int</code> type as <code>C.uint</code>;
see the <a href="/cmd/cgo">cgo documentation</a> for a complete list of
these numeric type names.
</p>
<p>
The one detail of this example we haven't examined yet is the comment
above the <code>import</code> statement.
</p>
{{code "/doc/progs/cgo1.go" `/\/\*/` `/STOP/`}}
<p>
Cgo recognizes this comment. Any lines starting
with <code>#cgo</code>
followed
by a space character are removed; these become directives for cgo.
The remaining lines are used as a header when compiling the C parts of
the package. In this case those lines are just a
single <code>#include</code>
statement, but they can be almost any C code. The <code>#cgo</code>
directives are
used to provide flags for the compiler and linker when building the C
parts of the package.
</p>
<p>
There is a limitation: if your program uses any <code>//export</code>
directives, then the C code in the comment may only include declarations
(<code>extern int f();</code>), not definitions (<code>int f() {
return 1; }</code>). You can use <code>//export</code> directives to
make Go functions accessible to C code.
</p>
<p>
The <code>#cgo</code> and <code>//export</code> directives are
documented in
the <a href="/cmd/cgo/">cgo documentation</a>.
</p>
<p>
<b>Strings and things</b>
</p>
<p>
Unlike Go, C doesn't have an explicit string type. Strings in C are
represented by a zero-terminated array of chars.
</p>
<p>
Conversion between Go and C strings is done with the
<code>C.CString</code>, <code>C.GoString</code>, and
<code>C.GoStringN</code> functions. These conversions make a copy of the
string data.
</p>
<p>
This next example implements a <code>Print</code> function that writes a
string to standard output using C's <code>fputs</code> function from the
<code>stdio</code> library:
</p>
{{code "/doc/progs/cgo3.go" `/package print/` `/END/`}}
<p>
Memory allocations made by C code are not known to Go's memory manager.
When you create a C string with <code>C.CString</code> (or any C memory
allocation) you must remember to free the memory when you're done with it
by calling <code>C.free</code>.
</p>
<p>
The call to <code>C.CString</code> returns a pointer to the start of the
char array, so before the function exits we convert it to an
<a href="/pkg/unsafe/#Pointer"><code>unsafe.Pointer</code></a> and release
the memory allocation with <code>C.free</code>. A common idiom in cgo programs
is to <a href="/doc/articles/defer_panic_recover.html"><code>defer</code></a>
the free immediately after allocating (especially when the code that follows
is more complex than a single function call), as in this rewrite of
<code>Print</code>:
</p>
{{code "/doc/progs/cgo4.go" `/func Print/` `/END/`}}
<p>
<b>Building cgo packages</b>
</p>
<p>
To build cgo packages, just use <a href="/cmd/go/#Compile_packages_and_dependencies">"
<code>go build</code>"</a> or
<a href="/cmd/go/#Compile_and_install_packages_and_dependencies">"<code>go install</code>
"</a> as usual. The go tool recognizes the special <code>"C"</code> import and automatically
uses cgo for those files.
</p>
<p>
<b>More cgo resources</b>
</p>
<p>
The <a href="/cmd/cgo/">cgo command</a> documentation has more detail about
the C pseudo-package and the build process. The <a href="/misc/cgo/">cgo examples</a>
in the Go tree demonstrate more advanced concepts.
</p>
<p>
For a simple, idiomatic example of a cgo-based package, see Russ Cox's <a
href="http://code.google.com/p/gosqlite/source/browse/sqlite/sqlite.go">gosqlite</a>.
Also, the Go Project Dashboard lists <a
href="https://godashboard.appspot.com/project?tag=cgo">several other
cgo packages</a>.
</p>
<p>
Finally, if you're curious as to how all this works internally, take a look
at the introductory comment of the runtime package's <a href="/src/pkg/runtime/cgocall.c">cgocall.c</a>.
</p>

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@@ -1,79 +0,0 @@
<!--{
"Title": "Go Concurrency Patterns: Timing out, moving on",
"Template": true
}-->
<p>
Concurrent programming has its own idioms. A good example is timeouts. Although
Go's channels do not support them directly, they are easy to implement. Say we
want to receive from the channel <code>ch</code>, but want to wait at most one
second for the value to arrive. We would start by creating a signalling channel
and launching a goroutine that sleeps before sending on the channel:
</p>
{{code "/doc/progs/timeout1.go" `/timeout :=/` `/STOP/`}}
<p>
We can then use a <code>select</code> statement to receive from either
<code>ch</code> or <code>timeout</code>. If nothing arrives on <code>ch</code>
after one second, the timeout case is selected and the attempt to read from
<cde>ch</cde> is abandoned.
</p>
{{code "/doc/progs/timeout1.go" `/select {/` `/STOP/`}}
<p>
The <code>timeout</code> channel is buffered with space for 1 value, allowing
the timeout goroutine to send to the channel and then exit. The goroutine
doesn't know (or care) whether the value is received. This means the goroutine
won't hang around forever if the <code>ch</code> receive happens before the
timeout is reached. The <code>timeout</code> channel will eventually be
deallocated by the garbage collector.
</p>
<p>
(In this example we used <code>time.Sleep</code> to demonstrate the mechanics
of goroutines and channels. In real programs you should use <code>
<a href="/pkg/time/#After">time.After</a></code>, a function that returns
a channel and sends on that channel after the specified duration.)
</p>
<p>
Let's look at another variation of this pattern. In this example we have a
program that reads from multiple replicated databases simultaneously. The
program needs only one of the answers, and it should accept the answer that
arrives first.
</p>
<p>
The function <code>Query</code> takes a slice of database connections and a
<code>query</code> string. It queries each of the databases in parallel and
returns the first response it receives:
</p>
{{code "/doc/progs/timeout2.go" `/func Query/` `/STOP/`}}
<p>
In this example, the closure does a non-blocking send, which it achieves by
using the send operation in <code>select</code> statement with a
<code>default</code> case. If the send cannot go through immediately the
default case will be selected. Making the send non-blocking guarantees that
none of the goroutines launched in the loop will hang around. However, if the
result arrives before the main function has made it to the receive, the send
could fail since no one is ready.
</p>
<p>
This problem is a textbook of example of what is known as a
<a href="https://en.wikipedia.org/wiki/Race_condition">race condition</a>, but
the fix is trivial. We just make sure to buffer the channel <code>ch</code> (by
adding the buffer length as the second argument to <a href="/pkg/builtin/#make">make</a>),
guaranteeing that the first send has a place to put the value. This ensures the
send will always succeed, and the first value to arrive will be retrieved
regardless of the order of execution.
</p>
<p>
These two examples demonstrate the simplicity with which Go can express complex
interactions between goroutines.
</p>

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@@ -1,197 +0,0 @@
<!--{
"Title": "Defer, Panic, and Recover",
"Template": true
}-->
<p>
Go has the usual mechanisms for control flow: if, for, switch, goto. It also
has the go statement to run code in a separate goroutine. Here I'd like to
discuss some of the less common ones: defer, panic, and recover.
</p>
<p>
A <b>defer statement</b> pushes a function call onto a list. The list of saved
calls is executed after the surrounding function returns. Defer is commonly
used to simplify functions that perform various clean-up actions.
</p>
<p>
For example, let's look at a function that opens two files and copies the
contents of one file to the other:
</p>
{{code "/doc/progs/defer.go" `/func CopyFile/` `/STOP/`}}
<p>
This works, but there is a bug. If the call to os.Create fails, the
function will return without closing the source file. This can be easily
remedied by putting a call to src.Close before the second return statement,
but if the function were more complex the problem might not be so easily
noticed and resolved. By introducing defer statements we can ensure that the
files are always closed:
</p>
{{code "/doc/progs/defer2.go" `/func CopyFile/` `/STOP/`}}
<p>
Defer statements allow us to think about closing each file right after opening
it, guaranteeing that, regardless of the number of return statements in the
function, the files <i>will</i> be closed.
</p>
<p>
The behavior of defer statements is straightforward and predictable. There are
three simple rules:
</p>
<p>
1. <i>A deferred function's arguments are evaluated when the defer statement is
evaluated.</i>
</p>
<p>
In this example, the expression "i" is evaluated when the Println call is
deferred. The deferred call will print "0" after the function returns.
</p>
{{code "/doc/progs/defer.go" `/func a/` `/STOP/`}}
<p>
2. <i>Deferred function calls are executed in Last In First Out order
</i>after<i> the surrounding function returns.</i>
</p>
<p>
This function prints "3210":
</p>
{{code "/doc/progs/defer.go" `/func b/` `/STOP/`}}
<p>
3. <i>Deferred functions may read and assign to the returning function's named
return values.</i>
</p>
<p>
In this example, a deferred function increments the return value i <i>after</i>
the surrounding function returns. Thus, this function returns 2:
</p>
{{code "/doc/progs/defer.go" `/func c/` `/STOP/`}}
<p>
This is convenient for modifying the error return value of a function; we will
see an example of this shortly.
</p>
<p>
<b>Panic</b> is a built-in function that stops the ordinary flow of control and
begins <i>panicking</i>. When the function F calls panic, execution of F stops,
any deferred functions in F are executed normally, and then F returns to its
caller. To the caller, F then behaves like a call to panic. The process
continues up the stack until all functions in the current goroutine have
returned, at which point the program crashes. Panics can be initiated by
invoking panic directly. They can also be caused by runtime errors, such as
out-of-bounds array accesses.
</p>
<p>
<b>Recover</b> is a built-in function that regains control of a panicking
goroutine. Recover is only useful inside deferred functions. During normal
execution, a call to recover will return nil and have no other effect. If the
current goroutine is panicking, a call to recover will capture the value given
to panic and resume normal execution.
</p>
<p>
Here's an example program that demonstrates the mechanics of panic and defer:
</p>
{{code "/doc/progs/defer2.go" `/package main/` `/STOP/`}}
<p>
The function g takes the int i, and panics if i is greater than 3, or else it
calls itself with the argument i+1. The function f defers a function that calls
recover and prints the recovered value (if it is non-nil). Try to picture what
the output of this program might be before reading on.
</p>
<p>
The program will output:
</p>
<pre>Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
Recovered in f 4
Returned normally from f.</pre>
<p>
If we remove the deferred function from f the panic is not recovered and
reaches the top of the goroutine's call stack, terminating the program. This
modified program will output:
</p>
<pre>Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
panic: 4
panic PC=0x2a9cd8
[stack trace omitted]</pre>
<p>
For a real-world example of <b>panic</b> and <b>recover</b>, see the
<a href="/pkg/encoding/json/">json package</a> from the Go standard library.
It decodes JSON-encoded data with a set of recursive functions.
When malformed JSON is encountered, the parser calls panic to unwind the
stack to the top-level function call, which recovers from the panic and returns
an appropriate error value (see the 'error' and 'unmarshal' methods of
the decodeState type in
<a href="/src/pkg/encoding/json/decode.go">decode.go</a>).
</p>
<p>
The convention in the Go libraries is that even when a package uses panic
internally, its external API still presents explicit error return values.
</p>
<p>
Other uses of <b>defer</b> (beyond the file.Close example given earlier)
include releasing a mutex:
</p>
<pre>mu.Lock()
defer mu.Unlock()</pre>
<p>
printing a footer:
</p>
<pre>printHeader()
defer printFooter()</pre>
<p>
and more.
</p>
<p>
In summary, the defer statement (with or without panic and recover) provides an
unusual and powerful mechanism for control flow. It can be used to model a
number of features implemented by special-purpose structures in other
programming languages. Try it out.
</p>

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@@ -1,316 +0,0 @@
<!--{
"Title": "Error Handling and Go",
"Template": true
}-->
<p>
If you have written any Go code you have probably encountered the built-in
<code>error</code> type. Go code uses <code>error</code> values to
indicate an abnormal state. For example, the <code>os.Open</code> function
returns a non-nil <code>error</code> value when it fails to open a file.
</p>
{{code "/doc/progs/error.go" `/func Open/`}}
<p>
The following code uses <code>os.Open</code> to open a file. If an error
occurs it calls <code>log.Fatal</code> to print the error message and stop.
</p>
{{code "/doc/progs/error.go" `/func openFile/` `/STOP/`}}
<p>
You can get a lot done in Go knowing just this about the <code>error</code>
type, but in this article we'll take a closer look at <code>error</code> and
discuss some good practices for error handling in Go.
</p>
<p>
<b>The error type</b>
</p>
<p>
The <code>error</code> type is an interface type. An <code>error</code>
variable represents any value that can describe itself as a string. Here is the
interface's declaration:
</p>
<pre>type error interface {
Error() string
}</pre>
<p>
The <code>error</code> type, as with all built in types, is
<a href="/doc/go_spec.html#Predeclared_identifiers">predeclared</a> in the
<a href="/doc/go_spec.html#Blocks">universe block</a>.
</p>
<p>
The most commonly-used <code>error</code> implementation is the
<a href="/pkg/errors/">errors</a> package's unexported <code>errorString</code> type.
</p>
{{code "/doc/progs/error.go" `/errorString/` `/STOP/`}}
<p>
You can construct one of these values with the <code>errors.New</code>
function. It takes a string that it converts to an <code>errors.errorString</code>
and returns as an <code>error</code> value.
</p>
{{code "/doc/progs/error.go" `/New/` `/STOP/`}}
<p>
Here's how you might use <code>errors.New</code>:
</p>
{{code "/doc/progs/error.go" `/func Sqrt/` `/STOP/`}}
<p>
A caller passing a negative argument to <code>Sqrt</code> receives a non-nil
<code>error</code> value (whose concrete representation is an
<code>errors.errorString</code> value). The caller can access the error string
("math: square root of...") by calling the <code>error</code>'s
<code>Error</code> method, or by just printing it:
</p>
{{code "/doc/progs/error.go" `/func printErr/` `/STOP/`}}
<p>
The <a href="/pkg/fmt/">fmt</a> package formats an <code>error</code> value
by calling its <code>Error() string</code> method.
</p>
<p>
It is the error implementation's responsibility to summarize the context.
The error returned by <code>os.Open</code> formats as "open /etc/passwd:
permission denied," not just "permission denied." The error returned by our
<code>Sqrt</code> is missing information about the invalid argument.
</p>
<p>
To add that information, a useful function is the <code>fmt</code> package's
<code>Errorf</code>. It formats a string according to <code>Printf</code>'s
rules and returns it as an <code>error</code> created by
<code>errors.New</code>.
</p>
{{code "/doc/progs/error.go" `/fmtError/` `/STOP/`}}
<p>
In many cases <code>fmt.Errorf</code> is good enough, but since
<code>error</code> is an interface, you can use arbitrary data structures as
error values, to allow callers to inspect the details of the error.
</p>
<p>
For instance, our hypothetical callers might want to recover the invalid
argument passed to <code>Sqrt</code>. We can enable that by defining a new
error implementation instead of using <code>errors.errorString</code>:
</p>
{{code "/doc/progs/error.go" `/type NegativeSqrtError/` `/STOP/`}}
<p>
A sophisticated caller can then use a
<a href="/doc/go_spec.html#Type_assertions">type assertion</a> to check for a
<code>NegativeSqrtError</code> and handle it specially, while callers that just
pass the error to <code>fmt.Println</code> or <code>log.Fatal</code> will see
no change in behavior.
</p>
<p>
As another example, the <a href="/pkg/encoding/json/">json</a> package specifies a
<code>SyntaxError</code> type that the <code>json.Decode</code> function
returns when it encounters a syntax error parsing a JSON blob.
</p>
{{code "/doc/progs/error.go" `/type SyntaxError/` `/STOP/`}}
<p>
The <code>Offset</code> field isn't even shown in the default formatting of the
error, but callers can use it to add file and line information to their error
messages:
</p>
{{code "/doc/progs/error.go" `/func decodeError/` `/STOP/`}}
<p>
(This is a slightly simplified version of some
<a href="http://camlistore.org/code/?p=camlistore.git;a=blob;f=lib/go/camli/jsonconfig/eval.go#l68">actual code</a>
from the <a href="http://camlistore.org">Camlistore</a> project.)
</p>
<p>
The <code>error</code> interface requires only a <code>Error</code> method;
specific error implementations might have additional methods. For instance, the
<a href="/pkg/net/">net</a> package returns errors of type
<code>error</code>, following the usual convention, but some of the error
implementations have additional methods defined by the <code>net.Error</code>
interface:
</p>
<pre>package net
type Error interface {
error
Timeout() bool // Is the error a timeout?
Temporary() bool // Is the error temporary?
}</pre>
<p>
Client code can test for a <code>net.Error</code> with a type assertion and
then distinguish transient network errors from permanent ones. For instance, a
web crawler might sleep and retry when it encounters a temporary error and give
up otherwise.
</p>
{{code "/doc/progs/error.go" `/func netError/` `/STOP/`}}
<p>
<b>Simplifying repetitive error handling</b>
</p>
<p>
In Go, error handling is important. The language's design and conventions
encourage you to explicitly check for errors where they occur (as distinct from
the convention in other languages of throwing exceptions and sometimes catching
them). In some cases this makes Go code verbose, but fortunately there are some
techniques you can use to minimize repetitive error handling.
</p>
<p>
Consider an <a href="http://code.google.com/appengine/docs/go/">App Engine</a>
application with an HTTP handler that retrieves a record from the datastore and
formats it with a template.
</p>
{{code "/doc/progs/error2.go" `/func init/` `/STOP/`}}
<p>
This function handles errors returned by the <code>datastore.Get</code>
function and <code>viewTemplate</code>'s <code>Execute</code> method. In both
cases, it presents a simple error message to the user with the HTTP status code
500 ("Internal Server Error"). This looks like a manageable amount of code, but
add some more HTTP handlers and you quickly end up with many copies of
identical error handling code.
</p>
<p>
To reduce the repetition we can define our own HTTP <code>appHandler</code>
type that includes an <code>error</code> return value:
</p>
{{code "/doc/progs/error3.go" `/type appHandler/`}}
<p>
Then we can change our <code>viewRecord</code> function to return errors:
</p>
{{code "/doc/progs/error3.go" `/func viewRecord/` `/STOP/`}}
<p>
This is simpler than the original version, but the <a
href="/pkg/net/http/">http</a> package doesn't understand functions that return
<code>error</code>.
To fix this we can implement the <code>http.Handler</code> interface's
<code>ServeHTTP</code> method on <code>appHandler</code>:
</p>
{{code "/doc/progs/error3.go" `/ServeHTTP/` `/STOP/`}}
<p>
The <code>ServeHTTP</code> method calls the <code>appHandler</code> function
and displays the returned error (if any) to the user. Notice that the method's
receiver, <code>fn</code>, is a function. (Go can do that!) The method invokes
the function by calling the receiver in the expression <code>fn(w, r)</code>.
</p>
<p>
Now when registering <code>viewRecord</code> with the http package we use the
<code>Handle</code> function (instead of <code>HandleFunc</code>) as
<code>appHandler</code> is an <code>http.Handler</code> (not an
<code>http.HandlerFunc</code>).
</p>
{{code "/doc/progs/error3.go" `/func init/` `/STOP/`}}
<p>
With this basic error handling infrastructure in place, we can make it more
user friendly. Rather than just displaying the error string, it would be better
to give the user a simple error message with an appropriate HTTP status code,
while logging the full error to the App Engine developer console for debugging
purposes.
</p>
<p>
To do this we create an <code>appError</code> struct containing an
<code>error</code> and some other fields:
</p>
{{code "/doc/progs/error4.go" `/type appError/` `/STOP/`}}
<p>
Next we modify the appHandler type to return <code>*appError</code> values:
</p>
{{code "/doc/progs/error4.go" `/type appHandler/`}}
<p>
(It's usually a mistake to pass back the concrete type of an error rather than
<code>error</code>,
for reasons discussed in <a href="/doc/go_faq.html#nil_error">the Go FAQ</a>,
but it's the right thing to do here because <code>ServeHTTP</code> is the only
place that sees the value and uses its contents.)
</p>
<p>
And make <code>appHandler</code>'s <code>ServeHTTP</code> method display the
<code>appError</code>'s <code>Message</code> to the user with the correct HTTP
status <code>Code</code> and log the full <code>Error</code> to the developer
console:
</p>
{{code "/doc/progs/error4.go" `/ServeHTTP/` `/STOP/`}}
<p>
Finally, we update <code>viewRecord</code> to the new function signature and
have it return more context when it encounters an error:
</p>
{{code "/doc/progs/error4.go" `/func viewRecord/` `/STOP/`}}
<p>
This version of <code>viewRecord</code> is the same length as the original, but
now each of those lines has specific meaning and we are providing a friendlier
user experience.
</p>
<p>
It doesn't end there; we can further improve the error handling in our
application. Some ideas:
</p>
<ul>
<li>give the error handler a pretty HTML template,
<li>make debugging easier by writing the stack trace to the HTTP response when
the user is an administrator,
<li>write a constructor function for <code>appError</code> that stores the
stack trace for easier debugging,
<li>recover from panics inside the <code>appHandler</code>, logging the error
to the console as "Critical," while telling the user "a serious error
has occurred." This is a nice touch to avoid exposing the user to inscrutable
error messages caused by programming errors.
See the <a href="defer_panic_recover.html">Defer, Panic, and Recover</a>
article for more details.
</ul>
<p>
<b>Conclusion</b>
</p>
<p>
Proper error handling is an essential requirement of good software. By
employing the techniques described in this post you should be able to write
more reliable and succinct Go code.
</p>

View File

@@ -1,265 +0,0 @@
<!--{
"title": "About the go command"
}-->
<p>The Go distribution includes a command, named
"<code><a href="/cmd/go/">go</a></code>", that
automates the downloading, building, installation, and testing of Go packages
and commands. This document talks about why we wrote a new command, what it
is, what it's not, and how to use it.</p>
<h2>Motivation</h2>
<p>You might have seen early Go talks in which Rob Pike jokes that the idea
for Go arose while waiting for a large Google server to compile. That
really was the motivation for Go: to build a language that worked well
for building the large software that Google writes and runs. It was
clear from the start that such a language must provide a way to
express dependencies between code libraries clearly, hence the package
grouping and the explicit import blocks. It was also clear from the
start that you might want arbitrary syntax for describing the code
being imported; this is why import paths are string literals.</p>
<p>An explicit goal for Go from the beginning was to be able to build Go
code using only the information found in the source itself, not
needing to write a makefile or one of the many modern replacements for
makefiles. If Go needed a configuration file to explain how to build
your program, then Go would have failed.</p>
<p>At first, there was no Go compiler, and the initial development
focused on building one and then building libraries for it. For
expedience, we postponed the automation of building Go code by using
make and writing makefiles. When compiling a single package involved
multiple invocations of the Go compiler, we even used a program to
write the makefiles for us. You can find it if you dig through the
repository history.</p>
<p>The purpose of the new go command is our return to this ideal, that Go
programs should compile without configuration or additional effort on
the part of the developer beyond writing the necessary import
statements.</p>
<h2>Configuration versus convention</h2>
<p>The way to achieve the simplicity of a configuration-free system is to
establish conventions. The system works only to the extent that those conventions
are followed. When we first launched Go, many people published packages that
had to be installed in certain places, under certain names, using certain build
tools, in order to be used. That's understandable: that's the way it works in
most other languages. Over the last few years we consistently reminded people
about the <code>goinstall</code> command
(now replaced by <a href="/cmd/go/#Download_and_install_packages_and_dependencies"><code>go get</code></a>)
and its conventions: first, that the import path is derived in a known way from
the URL of the source code; second, that that the place to store the sources in
the local file system is derived in a known way from the import path; third,
that each directory in a source tree corresponds to a single package; and
fourth, that the package is built using only information in the source code.
Today, the vast majority of packages follow these conventions.
The Go ecosystem is simpler and more powerful as a result.</p>
<p>We received many requests to allow a makefile in a package directory to
provide just a little extra configuration beyond what's in the source code.
But that would have introduced new rules. Because we did not accede to such
requests, we were able to write the go command and eliminate our use of make
or any other build system.</p>
<p>It is important to understand that the go command is not a general
build tool. It cannot be configured and it does not attempt to build
anything but Go packages. These are important simplifying
assumptions: they simplify not only the implementation but also, more
important, the use of the tool itself.</p>
<h2>Go's conventions</h2>
<p>The <code>go</code> command requires that code adheres to a few key,
well-established conventions.</p>
<p>First, the import path is derived in an known way from the URL of the
source code. For Bitbucket, GitHub, Google Code, and Launchpad, the
root directory of the repository is identified by the repository's
main URL, without the <code>http://</code> prefix. Subdirectories are named by
adding to that path. For example, the supplemental networking
libraries for Go are obtained by running</p>
<pre>
hg clone http://code.google.com/p/go.net
</pre>
<p>and thus the import path for the root directory of that repository is
"<code>code.google.com/p/go.net</code>". The websocket package is stored in a
subdirectory, so its import path is
"<code>code.google.com/p/go.net/websocket</code>".</p>
<p>These paths are on the long side, but in exchange we get an
automatically managed name space for import paths and the ability for
a tool like the go command to look at an unfamiliar import path and
deduce where to obtain the source code.</p>
<p>Second, the place to store sources in the local file system is derived
in a known way from the import path. Specifically, the first choice
is <code>$GOPATH/src/&lt;import-path&gt;</code>. If <code>$GOPATH</code> is
unset, the go command will fall back to storing source code alongside the
standard Go packages, in <code>$GOROOT/src/pkg/&lt;import-path&gt;</code>.
If <code>$GOPATH</code> is set to a list of paths, the go command tries
<code>&lt;dir&gt;/src/&lt;import-path&gt;</code> for each of the directories in
that list.</p>
<p>Each of those trees contains, by convention, a top-level directory named
"<code>bin</code>", for holding compiled executables, and a top-level directory
named "<code>pkg</code>", for holding compiled packages that can be imported,
and the "<code>src</code>" directory, for holding package source files.
Imposing this structure lets us keep each of these directory trees
self-contained: the compiled form and the sources are always near each
other.</p>
<p>These naming conventions also let us work in the reverse direction,
from a directory name to its import path. This mapping is important
for many of the go command's subcommands, as we'll see below.</p>
<p>Third, each directory in a source tree corresponds to a single
package. By restricting a directory to a single package, we don't have
to create hybrid import paths that specify first the directory and
then the package within that directory. Also, most file management
tools and UIs work on directories as fundamental units. Tying the
fundamental Go unit&mdash;the package&mdash;to file system structure means
that file system tools become Go package tools. Copying, moving, or
deleting a package corresponds to copying, moving, or deleting a
directory.</p>
<p>Fourth, each package is built using only the information present in
the source files. This makes it much more likely that the tool will
be able to adapt to changing build environments and conditions. For
example, if we allowed extra configuration such as compiler flags or
command line recipes, then that configuration would need to be updated
each time the build tools changed; it would also be inherently tied
to the use of a specific tool chain.</p>
<h2>Getting started with the go command</h2>
<p>Finally, a quick tour of how to use the go command, to supplement
the information in <a href="/doc/code.html">How to Write Go Code</a>,
which you might want to read first. Assuming you want
to keep your source code separate from the Go distribution source
tree, the first step is to set <code>$GOPATH</code>, the one piece of global
configuration that the go command needs. The <code>$GOPATH</code> can be a
list of directories, but by far the most common usage should be to set it to a
single directory. In particular, you do not need a separate entry in
<code>$GOPATH</code> for each of your projects. One <code>$GOPATH</code> can
support many projects.</p>
<p>Heres an example. Lets say we decide to keep our Go code in the directory
<code>$HOME/mygo</code>. We need to create that directory and set
<code>$GOPATH</code> accordingly.</p>
<pre>
$ mkdir $HOME/mygo
$ export GOPATH=$HOME/mygo
$
</pre>
<p>Into this directory, we now add some source code. Suppose we want to use
the indexing library from the codesearch project along with a left-leaning
red-black tree. We can install both with the "<code>go get</code>"
subcommand:</p>
<pre>
$ go get code.google.com/p/codesearch/index
$ go get github.com/petar/GoLLRB/llrb
$
</pre>
<p>Both of these projects are now downloaded and installed into our
<code>$GOPATH</code> directory. The one tree now contains the two directories
<code>src/code.google.com/p/codesearch/index/</code> and
<code>src/github.com/petar/GoLLRB/llrb/</code>, along with the compiled
packages (in <code>pkg/</code>) for those libraries and their dependencies.</p>
<p>Because we used version control systems (Mercurial and Git) to check
out the sources, the source tree also contains the other files in the
corresponding repositories, such as related packages. The "<code>go list</code>"
subcommand lists the import paths corresponding to its arguments, and
the pattern "<code>./...</code>" means start in the current directory
("<code>./</code>") and find all packages below that directory
("<code>...</code>"):</p>
<pre>
$ go list ./...
code.google.com/p/codesearch/cmd/cgrep
code.google.com/p/codesearch/cmd/cindex
code.google.com/p/codesearch/cmd/csearch
code.google.com/p/codesearch/index
code.google.com/p/codesearch/regexp
code.google.com/p/codesearch/sparse
github.com/petar/GoLLRB/example
github.com/petar/GoLLRB/llrb
$
</pre>
<p>We can also test those packages:</p>
<pre>
$ go test ./...
? code.google.com/p/codesearch/cmd/cgrep [no test files]
? code.google.com/p/codesearch/cmd/cindex [no test files]
? code.google.com/p/codesearch/cmd/csearch [no test files]
ok code.google.com/p/codesearch/index 0.239s
ok code.google.com/p/codesearch/regexp 0.021s
? code.google.com/p/codesearch/sparse [no test files]
? github.com/petar/GoLLRB/example [no test files]
ok github.com/petar/GoLLRB/llrb 0.231s
$
</pre>
<p>If a go subcommand is invoked with no paths listed, it operates on the
current directory:</p>
<pre>
$ cd $GOPATH/src/code.google.com/p/codesearch/regexp
$ go list
code.google.com/p/codesearch/regexp
$ go test -v
=== RUN TestNstateEnc
--- PASS: TestNstateEnc (0.00 seconds)
=== RUN TestMatch
--- PASS: TestMatch (0.01 seconds)
=== RUN TestGrep
--- PASS: TestGrep (0.00 seconds)
PASS
ok code.google.com/p/codesearch/regexp 0.021s
$ go install
$
</pre>
<p>That "<code>go install</code>" subcommand installs the latest copy of the
package into the pkg directory. Because the go command can analyze the
dependency graph, "<code>go install</code>" also installs any packages that
this package imports but that are out of date, recursively.</p>
<p>Notice that "<code>go install</code>" was able to determine the name of the
import path for the package in the current directory, because of the convention
for directory naming. It would be a little more convenient if we could pick
the name of the directory where we kept source code, and we probably wouldn't
pick such a long name, but that ability would require additional configuration
and complexity in the tool. Typing an extra directory name or two is a small
price to pay for the increased simplicity and power.</p>
<p>As the example shows, its fine to work with packages from many different
projects at once within a single <code>$GOPATH</code> root directory.</p>
<h2>Limitations</h2>
<p>As mentioned above, the go command is not a general-purpose build
tool. In particular, it does not have any facility for generating Go
source files during a build. Instead, if you want to use a tool like
yacc or the protocol buffer compiler, you will need to write a
makefile (or a configuration file for the build tool of your choice)
to generate the Go files and then check those generated source files
into your repository. This is more work for you, the package author,
but it is significantly less work for your users, who can use
"<code>go get</code>" without needing to obtain and build
any additional tools.</p>
<h2>More information</h2>
<p>For more information, read <a href="/doc/code.html">How to Write Go Code</a>
and see the <a href="/cmd/go/">go command documentation</a>.</p>

View File

@@ -1,315 +0,0 @@
<!--{
"Title": "Gobs of data",
"Template": true
}-->
<p>
To transmit a data structure across a network or to store it in a file, it must
be encoded and then decoded again. There are many encodings available, of
course: <a href="http://www.json.org/">JSON</a>,
<a href="http://www.w3.org/XML/">XML</a>, Google's
<a href="http://code.google.com/p/protobuf">protocol buffers</a>, and more.
And now there's another, provided by Go's <a href="/pkg/encoding/gob/">gob</a>
package.
</p>
<p>
Why define a new encoding? It's a lot of work and redundant at that. Why not
just use one of the existing formats? Well, for one thing, we do! Go has
<a href="/pkg/">packages</a> supporting all the encodings just mentioned (the
<a href="http://code.google.com/p/goprotobuf">protocol buffer package</a> is in
a separate repository but it's one of the most frequently downloaded). And for
many purposes, including communicating with tools and systems written in other
languages, they're the right choice.
</p>
<p>
But for a Go-specific environment, such as communicating between two servers
written in Go, there's an opportunity to build something much easier to use and
possibly more efficient.
</p>
<p>
Gobs work with the language in a way that an externally-defined,
language-independent encoding cannot. At the same time, there are lessons to be
learned from the existing systems.
</p>
<p>
<b>Goals</b>
</p>
<p>
The gob package was designed with a number of goals in mind.
</p>
<p>
First, and most obvious, it had to be very easy to use. First, because Go has
reflection, there is no need for a separate interface definition language or
"protocol compiler". The data structure itself is all the package should need
to figure out how to encode and decode it. On the other hand, this approach
means that gobs will never work as well with other languages, but that's OK:
gobs are unashamedly Go-centric.
</p>
<p>
Efficiency is also important. Textual representations, exemplified by XML and
JSON, are too slow to put at the center of an efficient communications network.
A binary encoding is necessary.
</p>
<p>
Gob streams must be self-describing. Each gob stream, read from the beginning,
contains sufficient information that the entire stream can be parsed by an
agent that knows nothing a priori about its contents. This property means that
you will always be able to decode a gob stream stored in a file, even long
after you've forgotten what data it represents.
</p>
<p>
There were also some things to learn from our experiences with Google protocol
buffers.
</p>
<p>
<b>Protocol buffer misfeatures</b>
</p>
<p>
Protocol buffers had a major effect on the design of gobs, but have three
features that were deliberately avoided. (Leaving aside the property that
protocol buffers aren't self-describing: if you don't know the data definition
used to encode a protocol buffer, you might not be able to parse it.)
</p>
<p>
First, protocol buffers only work on the data type we call a struct in Go. You
can't encode an integer or array at the top level, only a struct with fields
inside it. That seems a pointless restriction, at least in Go. If all you want
to send is an array of integers, why should you have to put it into a
struct first?
</p>
<p>
Next, a protocol buffer definition may specify that fields <code>T.x</code> and
<code>T.y</code> are required to be present whenever a value of type
<code>T</code> is encoded or decoded. Although such required fields may seem
like a good idea, they are costly to implement because the codec must maintain a
separate data structure while encoding and decoding, to be able to report when
required fields are missing. They're also a maintenance problem. Over time, one
may want to modify the data definition to remove a required field, but that may
cause existing clients of the data to crash. It's better not to have them in the
encoding at all. (Protocol buffers also have optional fields. But if we don't
have required fields, all fields are optional and that's that. There will be
more to say about optional fields a little later.)
</p>
<p>
The third protocol buffer misfeature is default values. If a protocol buffer
omits the value for a "defaulted" field, then the decoded structure behaves as
if the field were set to that value. This idea works nicely when you have
getter and setter methods to control access to the field, but is harder to
handle cleanly when the container is just a plain idiomatic struct. Required
fields are also tricky to implement: where does one define the default values,
what types do they have (is text UTF-8? uninterpreted bytes? how many bits in a
float?) and despite the apparent simplicity, there were a number of
complications in their design and implementation for protocol buffers. We
decided to leave them out of gobs and fall back to Go's trivial but effective
defaulting rule: unless you set something otherwise, it has the "zero value"
for that type - and it doesn't need to be transmitted.
</p>
<p>
So gobs end up looking like a sort of generalized, simplified protocol buffer.
How do they work?
</p>
<p>
<b>Values</b>
</p>
<p>
The encoded gob data isn't about <code>int8</code>s and <code>uint16</code>s.
Instead, somewhat analogous to constants in Go, its integer values are abstract,
sizeless numbers, either signed or unsigned. When you encode an
<code>int8</code>, its value is transmitted as an unsized, variable-length
integer. When you encode an <code>int64</code>, its value is also transmitted as
an unsized, variable-length integer. (Signed and unsigned are treated
distinctly, but the same unsized-ness applies to unsigned values too.) If both
have the value 7, the bits sent on the wire will be identical. When the receiver
decodes that value, it puts it into the receiver's variable, which may be of
arbitrary integer type. Thus an encoder may send a 7 that came from an
<code>int8</code>, but the receiver may store it in an <code>int64</code>. This
is fine: the value is an integer and as a long as it fits, everything works. (If
it doesn't fit, an error results.) This decoupling from the size of the variable
gives some flexibility to the encoding: we can expand the type of the integer
variable as the software evolves, but still be able to decode old data.
</p>
<p>
This flexibility also applies to pointers. Before transmission, all pointers are
flattened. Values of type <code>int8</code>, <code>*int8</code>,
<code>**int8</code>, <code>****int8</code>, etc. are all transmitted as an
integer value, which may then be stored in <code>int</code> of any size, or
<code>*int</code>, or <code>******int</code>, etc. Again, this allows for
flexibility.
</p>
<p>
Flexibility also happens because, when decoding a struct, only those fields
that are sent by the encoder are stored in the destination. Given the value
</p>
{{code "/doc/progs/gobs1.go" `/type T/` `/STOP/`}}
<p>
the encoding of <code>t</code> sends only the 7 and 8. Because it's zero, the
value of <code>Y</code> isn't even sent; there's no need to send a zero value.
</p>
<p>
The receiver could instead decode the value into this structure:
</p>
{{code "/doc/progs/gobs1.go" `/type U/` `/STOP/`}}
<p>
and acquire a value of <code>u</code> with only <code>X</code> set (to the
address of an <code>int8</code> variable set to 7); the <code>Z</code> field is
ignored - where would you put it? When decoding structs, fields are matched by
name and compatible type, and only fields that exist in both are affected. This
simple approach finesses the "optional field" problem: as the type
<code>T</code> evolves by adding fields, out of date receivers will still
function with the part of the type they recognize. Thus gobs provide the
important result of optional fields - extensibility - without any additional
mechanism or notation.
</p>
<p>
From integers we can build all the other types: bytes, strings, arrays, slices,
maps, even floats. Floating-point values are represented by their IEEE 754
floating-point bit pattern, stored as an integer, which works fine as long as
you know their type, which we always do. By the way, that integer is sent in
byte-reversed order because common values of floating-point numbers, such as
small integers, have a lot of zeros at the low end that we can avoid
transmitting.
</p>
<p>
One nice feature of gobs that Go makes possible is that they allow you to define
your own encoding by having your type satisfy the
<a href="/pkg/encoding/gob/#GobEncoder">GobEncoder</a> and
<a href="/pkg/encoding/gob/#GobDecoder">GobDecoder</a> interfaces, in a manner
analogous to the <a href="/pkg/encoding/json/">JSON</a> package's
<a href="/pkg/encoding/json/#Marshaler">Marshaler</a> and
<a href="/pkg/encoding/json/#Unmarshaler">Unmarshaler</a> and also to the
<a href="/pkg/fmt/#Stringer">Stringer</a> interface from
<a href="/pkg/fmt/">package fmt</a>. This facility makes it possible to
represent special features, enforce constraints, or hide secrets when you
transmit data. See the <a href="/pkg/encoding/gob/">documentation</a> for
details.
</p>
<p>
<b>Types on the wire</b>
</p>
<p>
The first time you send a given type, the gob package includes in the data
stream a description of that type. In fact, what happens is that the encoder is
used to encode, in the standard gob encoding format, an internal struct that
describes the type and gives it a unique number. (Basic types, plus the layout
of the type description structure, are predefined by the software for
bootstrapping.) After the type is described, it can be referenced by its type
number.
</p>
<p>
Thus when we send our first type <code>T</code>, the gob encoder sends a
description of <code>T</code> and tags it with a type number, say 127. All
values, including the first, are then prefixed by that number, so a stream of
<code>T</code> values looks like:
</p>
<pre>
("define type id" 127, definition of type T)(127, T value)(127, T value), ...
</pre>
<p>
These type numbers make it possible to describe recursive types and send values
of those types. Thus gobs can encode types such as trees:
</p>
{{code "/doc/progs/gobs1.go" `/type Node/` `/STOP/`}}
<p>
(It's an exercise for the reader to discover how the zero-defaulting rule makes
this work, even though gobs don't represent pointers.)
</p>
<p>
With the type information, a gob stream is fully self-describing except for the
set of bootstrap types, which is a well-defined starting point.
</p>
<p>
<b>Compiling a machine</b>
</p>
<p>
The first time you encode a value of a given type, the gob package builds a
little interpreted machine specific to that data type. It uses reflection on
the type to construct that machine, but once the machine is built it does not
depend on reflection. The machine uses package unsafe and some trickery to
convert the data into the encoded bytes at high speed. It could use reflection
and avoid unsafe, but would be significantly slower. (A similar high-speed
approach is taken by the protocol buffer support for Go, whose design was
influenced by the implementation of gobs.) Subsequent values of the same type
use the already-compiled machine, so they can be encoded right away.
</p>
<p>
Decoding is similar but harder. When you decode a value, the gob package holds
a byte slice representing a value of a given encoder-defined type to decode,
plus a Go value into which to decode it. The gob package builds a machine for
that pair: the gob type sent on the wire crossed with the Go type provided for
decoding. Once that decoding machine is built, though, it's again a
reflectionless engine that uses unsafe methods to get maximum speed.
</p>
<p>
<b>Use</b>
</p>
<p>
There's a lot going on under the hood, but the result is an efficient,
easy-to-use encoding system for transmitting data. Here's a complete example
showing differing encoded and decoded types. Note how easy it is to send and
receive values; all you need to do is present values and variables to the
<a href="/pkg/encoding/gob/">gob package</a> and it does all the work.
</p>
{{code "/doc/progs/gobs2.go" `/package main/` `$`}}
<p>
You can compile and run this example code in the
<a href="http://play.golang.org/p/_-OJV-rwMq">Go Playground</a>.
</p>
<p>
The <a href="/pkg/net/rpc/">rpc package</a> builds on gobs to turn this
encode/decode automation into transport for method calls across the network.
That's a subject for another article.
</p>
<p>
<b>Details</b>
</p>
<p>
The <a href="/pkg/encoding/gob/">gob package documentation</a>, especially the
file <a href="/src/pkg/encoding/gob/doc.go">doc.go</a>, expands on many of the
details described here and includes a full worked example showing how the
encoding represents data. If you are interested in the innards of the gob
implementation, that's a good place to start.
</p>

View File

@@ -1,139 +0,0 @@
<!--{
"Title": "Godoc: documenting Go code",
"Template": true
}-->
<p>
The Go project takes documentation seriously. Documentation is a huge part of
making software accessible and maintainable. Of course it must be well-written
and accurate, but it also must be easy to write and to maintain. Ideally, it
should be coupled to the code itself so the documentation evolves along with the
code. The easier it is for programmers to produce good documentation, the better
for everyone.
</p>
<p>
To that end, we have developed the <a href="/cmd/godoc/">godoc</a> documentation
tool. This article describes godoc's approach to documentation, and explains how
you can use our conventions and tools to write good documentation for your own
projects.
</p>
<p>
Godoc parses Go source code - including comments - and produces documentation as
HTML or plain text. The end result is documentation tightly coupled with the
code it documents. For example, through godoc's web interface you can navigate
from a function's <a href="/pkg/strings/#HasPrefix">documentation</a> to its
<a href="/src/pkg/strings/strings.go?#L312">implementation</a> with one click.
</p>
<p>
Godoc is conceptually related to Python's
<a href="http://www.python.org/dev/peps/pep-0257/">Docstring</a> and Java's
<a href="http://www.oracle.com/technetwork/java/javase/documentation/index-jsp-135444.html">Javadoc</a>,
but its design is simpler. The comments read by godoc are not language
constructs (as with Docstring) nor must they have their own machine-readable
syntax (as with Javadoc). Godoc comments are just good comments, the sort you
would want to read even if godoc didn't exist.
</p>
<p>
The convention is simple: to document a type, variable, constant, function, or
even a package, write a regular comment directly preceding its declaration, with
no intervening blank line. Godoc will then present that comment as text
alongside the item it documents. For example, this is the documentation for the
<code>fmt</code> package's <a href="/pkg/fmt/#Fprint"><code>Fprint</code></a>
function:
</p>
{{code "/src/pkg/fmt/print.go" `/Fprint formats using the default/` `/func Fprint/`}}
<p>
Notice this comment is a complete sentence that begins with the name of the
element it describes. This important convention allows us to generate
documentation in a variety of formats, from plain text to HTML to UNIX man
pages, and makes it read better when tools truncate it for brevity, such as when
they extract the first line or sentence.
</p>
<p>
Comments on package declarations should provide general package documentation.
These comments can be short, like the <a href="/pkg/sort/"><code>sort</code></a>
package's brief description:
</p>
{{code "/src/pkg/sort/sort.go" `/Package sort provides/` `/package sort/`}}
<p>
They can also be detailed like the <a href="/pkg/encoding/gob/">gob package</a>'s
overview. That package uses another convention for packages
that need large amounts of introductory documentation: the package comment is
placed in its own file, <a href="/src/pkg/encoding/gob/doc.go">doc.go</a>, which
contains only those comments and a package clause.
</p>
<p>
When writing package comments of any size, keep in mind that their first
sentence will appear in godoc's <a href="/pkg/">package list</a>.
</p>
<p>
Comments that are not adjacent to a top-level declaration are omitted from
godoc's output, with one notable exception. Top-level comments that begin with
the word <code>"BUG(who)”</code> are recognized as known bugs, and included in
the "Bugs” section of the package documentation. The "who” part should be the
user name of someone who could provide more information. For example, this is a
known issue from the <a href="/pkg/bytes/#bugs">bytes package</a>:
</p>
<pre>
// BUG(r): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
</pre>
<p>
Godoc treats executable commands somewhat differently. Instead of inspecting the
command source code, it looks for a Go source file belonging to the special
package "documentation”. The comment on the "package documentation” clause is
used as the command's documentation. For example, see the
<a href="/cmd/godoc/">godoc documentation</a> and its corresponding
<a href="/src/cmd/godoc/doc.go">doc.go</a> file.
</p>
<p>
There are a few formatting rules that Godoc uses when converting comments to
HTML:
</p>
<ul>
<li>
Subsequent lines of text are considered part of the same paragraph; you must
leave a blank line to separate paragraphs.
</li>
<li>
Pre-formatted text must be indented relative to the surrounding comment text
(see gob's <a href="/src/pkg/encoding/gob/doc.go">doc.go</a> for an example).
</li>
<li>
URLs will be converted to HTML links; no special markup is necessary.
</li>
</ul>
<p>
Note that none of these rules requires you to do anything out of the ordinary.
</p>
<p>
In fact, the best thing about godoc's minimal approach is how easy it is to use.
As a result, a lot of Go code, including all of the standard library, already
follows the conventions.
</p>
<p>
Your own code can present good documentation just by having comments as
described above. Any Go packages installed inside <code>$GOROOT/src/pkg</code>
and any <code>GOPATH</code> work spaces will already be accessible via godoc's
command-line and HTTP interfaces, and you can specify additional paths for
indexing via the <code>-path</code> flag or just by running <code>"godoc ."</code>
in the source directory. See the <a href="/cmd/godoc/">godoc documentation</a>
for more details.
</p>

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@@ -1,348 +0,0 @@
<!--{
"Title": "Go's Declaration Syntax"
}-->
<p>
Newcomers to Go wonder why the declaration syntax is different from the
tradition established in the C family. In this post we'll compare the
two approaches and explain why Go's declarations look as they do.
</p>
<p>
<b>C syntax</b>
</p>
<p>
First, let's talk about C syntax. C took an unusual and clever approach
to declaration syntax. Instead of describing the types with special
syntax, one writes an expression involving the item being declared, and
states what type that expression will have. Thus
</p>
<pre>
int x;
</pre>
<p>
declares x to be an int: the expression 'x' will have type int. In
general, to figure out how to write the type of a new variable, write an
expression involving that variable that evaluates to a basic type, then
put the basic type on the left and the expression on the right.
</p>
<p>
Thus, the declarations
</p>
<pre>
int *p;
int a[3];
</pre>
<p>
state that p is a pointer to int because '*p' has type int, and that a
is an array of ints because a[3] (ignoring the particular index value,
which is punned to be the size of the array) has type int.
</p>
<p>
What about functions? Originally, C's function declarations wrote the
types of the arguments outside the parens, like this:
</p>
<pre>
int main(argc, argv)
int argc;
char *argv[];
{ /* ... */ }
</pre>
<p>
Again, we see that main is a function because the expression main(argc,
argv) returns an int. In modern notation we'd write
</p>
<pre>
int main(int argc, char *argv[]) { /* ... */ }
</pre>
<p>
but the basic structure is the same.
</p>
<p>
This is a clever syntactic idea that works well for simple types but can
get confusing fast. The famous example is declaring a function pointer.
Follow the rules and you get this:
</p>
<pre>
int (*fp)(int a, int b);
</pre>
<p>
Here, fp is a pointer to a function because if you write the expression
(*fp)(a, b) you'll call a function that returns int. What if one of fp's
arguments is itself a function?
</p>
<pre>
int (*fp)(int (*ff)(int x, int y), int b)
</pre>
<p>
That's starting to get hard to read.
</p>
<p>
Of course, we can leave out the name of the parameters when we declare a
function, so main can be declared
</p>
<pre>
int main(int, char *[])
</pre>
<p>
Recall that argv is declared like this,
</p>
<pre>
char *argv[]
</pre>
<p>
so you drop the name from the <em>middle</em> of its declaration to construct
its type. It's not obvious, though, that you declare something of type
char *[] by putting its name in the middle.
</p>
<p>
And look what happens to fp's declaration if you don't name the
parameters:
</p>
<pre>
int (*fp)(int (*)(int, int), int)
</pre>
<p>
Not only is it not obvious where to put the name inside
</p>
<pre>
int (*)(int, int)
</pre>
<p>
it's not exactly clear that it's a function pointer declaration at all.
And what if the return type is a function pointer?
</p>
<pre>
int (*(*fp)(int (*)(int, int), int))(int, int)
</pre>
<p>
It's hard even to see that this declaration is about fp.
</p>
<p>
You can construct more elaborate examples but these should illustrate
some of the difficulties that C's declaration syntax can introduce.
</p>
<p>
There's one more point that needs to be made, though. Because type and
declaration syntax are the same, it can be difficult to parse
expressions with types in the middle. This is why, for instance, C casts
always parenthesize the type, as in
</p>
<pre>
(int)M_PI
</pre>
<p>
<b>Go syntax</b>
</p>
<p>
Languages outside the C family usually use a distinct type syntax in
declarations. Although it's a separate point, the name usually comes
first, often followed by a colon. Thus our examples above become
something like (in a fictional but illustrative language)
</p>
<pre>
x: int
p: pointer to int
a: array[3] of int
</pre>
<p>
These declarations are clear, if verbose - you just read them left to
right. Go takes its cue from here, but in the interests of brevity it
drops the colon and removes some of the keywords:
</p>
<pre>
x int
p *int
a [3]int
</pre>
<p>
There is no direct correspondence between the look of [3]int and how to
use a in an expression. (We'll come back to pointers in the next
section.) You gain clarity at the cost of a separate syntax.
</p>
<p>
Now consider functions. Let's transcribe the declaration for main, even
though the main function in Go takes no arguments:
</p>
<pre>
func main(argc int, argv *[]byte) int
</pre>
<p>
Superficially that's not much different from C, but it reads well from
left to right:
</p>
<p>
<em>function main takes an int and a pointer to a slice of bytes and returns an int.</em>
</p>
<p>
Drop the parameter names and it's just as clear - they're always first
so there's no confusion.
</p>
<pre>
func main(int, *[]byte) int
</pre>
<p>
One value of this left-to-right style is how well it works as the types
become more complex. Here's a declaration of a function variable
(analogous to a function pointer in C):
</p>
<pre>
f func(func(int,int) int, int) int
</pre>
<p>
Or if f returns a function:
</p>
<pre>
f func(func(int,int) int, int) func(int, int) int
</pre>
<p>
It still reads clearly, from left to right, and it's always obvious
which name is being declared - the name comes first.
</p>
<p>
The distinction between type and expression syntax makes it easy to
write and invoke closures in Go:
</p>
<pre>
sum := func(a, b int) int { return a+b } (3, 4)
</pre>
<p>
<b>Pointers</b>
</p>
<p>
Pointers are the exception that proves the rule. Notice that in arrays
and slices, for instance, Go's type syntax puts the brackets on the left
of the type but the expression syntax puts them on the right of the
expression:
</p>
<pre>
var a []int
x = a[1]
</pre>
<p>
For familiarity, Go's pointers use the * notation from C, but we could
not bring ourselves to make a similar reversal for pointer types. Thus
pointers work like this
</p>
<pre>
var p *int
x = *p
</pre>
<p>
We couldn't say
</p>
<pre>
var p *int
x = p*
</pre>
<p>
because that postfix * would conflate with multiplication. We could have
used the Pascal ^, for example:
</p>
<pre>
var p ^int
x = p^
</pre>
<p>
and perhaps we should have (and chosen another operator for xor),
because the prefix asterisk on both types and expressions complicates
things in a number of ways. For instance, although one can write
</p>
<pre>
[]int("hi")
</pre>
<p>
as a conversion, one must parenthesize the type if it starts with a *:
</p>
<pre>
(*int)(nil)
</pre>
<p>
Had we been willing to give up * as pointer syntax, those parentheses
would be unnecessary.
</p>
<p>
So Go's pointer syntax is tied to the familiar C form, but those ties
mean that we cannot break completely from using parentheses to
disambiguate types and expressions in the grammar.
</p>
<p>
Overall, though, we believe Go's type syntax is easier to understand
than C's, especially when things get complicated.
</p>
<p>
<b>Notes</b>
</p>
<p>
Go's declarations read left to right. It's been pointed out that C's
read in a spiral! See <a href="http://c-faq.com/decl/spiral.anderson.html">
The "Clockwise/Spiral Rule"</a> by David Anderson.
</p>

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<!--{
"Title": "The Go image/draw package",
"Template": true
}-->
<p>
<a href="/pkg/image/draw/">Package image/draw</a> defines
only one operation: drawing a source image onto a destination
image, through an optional mask image. This one operation is
surprisingly versatile and can perform a number of common image
manipulation tasks elegantly and efficiently.
</p>
<p>
Composition is performed pixel by pixel in the style of the Plan 9
graphics library and the X Render extension. The model is based on
the classic "Compositing Digital Images" paper by Porter and Duff,
with an additional mask parameter: <code>dst = (src IN mask) OP dst</code>.
For a fully opaque mask, this reduces to the original Porter-Duff
formula: <code>dst = src OP dst</code>. In Go, a nil mask image is equivalent
to an infinitely sized, fully opaque mask image.
</p>
<p>
The Porter-Duff paper presented
<a href="http://www.w3.org/TR/SVGCompositing/examples/compop-porterduff-examples.png">12 different composition operators</a>,
but with an explicit mask, only 2 of these are needed in practice:
source-over-destination and source. In Go, these operators are
represented by the <code>Over</code> and <code>Src</code> constants. The <code>Over</code> operator
performs the natural layering of a source image over a destination
image: the change to the destination image is smaller where the
source (after masking) is more transparent (that is, has lower
alpha). The <code>Src</code> operator merely copies the source (after masking)
with no regard for the destination image's original content. For
fully opaque source and mask images, the two operators produce the
same output, but the <code>Src</code> operator is usually faster.
</p>
<p><b>Geometric Alignment</b></p>
<p>
Composition requires associating destination pixels with source and
mask pixels. Obviously, this requires destination, source and mask
images, and a composition operator, but it also requires specifying
what rectangle of each image to use. Not every drawing should write
to the entire destination: when updating an animating image, it is
more efficient to only draw the parts of the image that have
changed. Not every drawing should read from the entire source: when
using a sprite that combines many small images into one large one,
only a part of the image is needed. Not every drawing should read
from the entire mask: a mask image that collects a font's glyphs is
similar to a sprite. Thus, drawing also needs to know three
rectangles, one for each image. Since each rectangle has the same
width and height, it suffices to pass a destination rectangle `r`
and two points <code>sp</code> and <code>mp</code>: the source rectangle is equal to <code>r</code>
translated so that <code>r.Min</code> in the destination image aligns with
<code>sp</code> in the source image, and similarly for <code>mp</code>. The effective
rectangle is also clipped to each image's bounds in their
respective co-ordinate space.
</p>
<p>
<img src="image-20.png">
</p>
<p>
The <a href="/pkg/image/draw/#DrawMask"><code>DrawMask</code></a>
function takes seven arguments, but an explicit mask and mask-point
are usually unnecessary, so the
<a href="/pkg/image/draw/#Draw"><code>Draw</code></a> function takes five:
</p>
<pre>
// Draw calls DrawMask with a nil mask.
func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op)
func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point,
mask image.Image, mp image.Point, op Op)
</pre>
<p>
The destination image must be mutable, so the image/draw package
defines a <a href="/pkg/image/draw/#Image"><code>draw.Image</code></a>
interface which has a <code>Set</code> method.
</p>
{{code "../src/pkg/image/draw/draw.go" `/type Image/` `/}/`}}
<p><b>Filling a Rectangle</b></p>
<p>
To fill a rectangle with a solid color, use an <code>image.Uniform</code>
source. The <code>ColorImage</code> type re-interprets a <code>Color</code> as a
practically infinite-sized <code>Image</code> of that color. For those
familiar with the design of Plan 9's draw library, there is no need
for an explicit "repeat bit" in Go's slice-based image types; the
concept is subsumed by <code>Uniform</code>.
</p>
{{code "/doc/progs/image_draw.go" `/ZERO/` `/STOP/`}}
<p>
To initialize a new image to all-blue:
</p>
{{code "/doc/progs/image_draw.go" `/BLUE/` `/STOP/`}}
<p>
To reset an image to transparent (or black, if the destination
image's color model cannot represent transparency), use
<code>image.Transparent</code>, which is an <code>image.Uniform</code>:
</p>
{{code "/doc/progs/image_draw.go" `/RESET/` `/STOP/`}}
<p>
<img src="image-2a.png">
</p>
<p><b>Copying an Image</b></p>
<p>
To copy from a rectangle <code>sr</code> in the source image to a rectangle
starting at a point <code>dp</code> in the destination, convert the source
rectangle into the destination image's co-ordinate space:
</p>
{{code "/doc/progs/image_draw.go" `/RECT/` `/STOP/`}}
<p>
Alternatively:
</p>
{{code "/doc/progs/image_draw.go" `/RECT2/` `/STOP/`}}
<p>
To copy the entire source image, use <code>sr = src.Bounds()</code>.
</p>
<p>
<img src="image-2b.png">
</p>
<p><b>Scrolling an Image</b></p>
<p>
Scrolling an image is just copying an image to itself, with
different destination and source rectangles. Overlapping
destination and source images are perfectly valid, just as Go's
built-in copy function can handle overlapping destination and
source slices. To scroll an image m by 20 pixels:
</p>
{{code "/doc/progs/image_draw.go" `/SCROLL/` `/STOP/`}}
<p><img src="image-2c.png"></p>
<p><b>Converting an Image to RGBA</b></p>
<p>
The result of decoding an image format might not be an
<code>image.RGBA</code>: decoding a GIF results in an <code>image.Paletted</code>,
decoding a JPEG results in a <code>ycbcr.YCbCr</code>, and the result of
decoding a PNG depends on the image data. To convert any image to
an <code>image.RGBA</code>:
</p>
{{code "/doc/progs/image_draw.go" `/CONV/` `/STOP/`}}
<p>
<img src="image-2d.png">
</p>
<p><b>Drawing Through a Mask</b></p>
<p>
To draw an image through a circular mask with center <code>p</code> and radius
<code>r</code>:
</p>
{{code "/doc/progs/image_draw.go" `/CIRCLESTRUCT/` `/STOP/`}}
{{code "/doc/progs/image_draw.go" `/CIRCLE2/` `/STOP/`}}
<p>
<img src="image-2e.png">
</p>
<p><b>Drawing Font Glyphs</b></p>
<p>
To draw a font glyph in blue starting from a point <code>p</code>, draw with
an <code>image.ColorImage</code> source and an <code>image.Alpha mask</code>. For
simplicity, we aren't performing any sub-pixel positioning or
rendering, or correcting for a font's height above a baseline.
</p>
{{code "/doc/progs/image_draw.go" `/GLYPH/` `/STOP/`}}
<p>
<img src="image-2f.png">
</p>
<p><b>Performance</b></p>
<p>
The image/draw package implementation demonstrates how to provide
an image manipulation function that is both general purpose, yet
efficient for common cases. The <code>DrawMask</code> function takes arguments
of interface types, but immediately makes type assertions that its
arguments are of specific struct types, corresponding to common
operations like drawing one <code>image.RGBA</code> image onto another, or
drawing an <code>image.Alpha</code> mask (such as a font glyph) onto an
<code>image.RGBA</code> image. If a type assertion succeeds, that type
information is used to run a specialized implementation of the
general algorithm. If the assertions fail, the fallback code path
uses the generic <code>At</code> and <code>Set</code> methods. The fast-paths are purely
a performance optimization; the resultant destination image is the
same either way. In practice, only a small number of special cases
are necessary to support typical applications.
</p>

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@@ -1,312 +0,0 @@
<!--{
"Title": "The Go image package",
"Template": true
}-->
<p>
The <a href="/pkg/image/">image</a> and
<a href="/pkg/image/color/">image/color</a> packages define a number of types:
<code>color.Color</code> and <code>color.Model</code> describe colors,
<code>image.Point</code> and <code>image.Rectangle</code> describe basic 2-D
geometry, and <code>image.Image</code> brings the two concepts together to
represent a rectangular grid of colors. A
<a href="/doc/articles/image_draw.html">separate article</a> covers image
composition with the <a href="/pkg/image/draw/">image/draw</a> package.
</p>
<p>
<b>Colors and Color Models</b>
</p>
<p>
<a href="/pkg/image/color/#Color">Color</a> is an interface that defines the minimal
method set of any type that can be considered a color: one that can be converted
to red, green, blue and alpha values. The conversion may be lossy, such as
converting from CMYK or YCbCr color spaces.
</p>
{{code "/src/pkg/image/color/color.go" `/type Color interface/` `/^}/`}}
<p>
There are three important subtleties about the return values. First, the red,
green and blue are alpha-premultiplied: a fully saturated red that is also 25%
transparent is represented by RGBA returning a 75% r. Second, the channels have
a 16-bit effective range: 100% red is represented by RGBA returning an r of
65535, not 255, so that converting from CMYK or YCbCr is not as lossy. Third,
the type returned is <code>uint32</code>, even though the maximum value is 65535, to
guarantee that multiplying two values together won't overflow. Such
multiplications occur when blending two colors according to an alpha mask from a
third color, in the style of
<a href="https://en.wikipedia.org/wiki/Alpha_compositing">Porter and Duff's</a>
classic algebra:
</p>
<pre>
dstr, dstg, dstb, dsta := dst.RGBA()
srcr, srcg, srcb, srca := src.RGBA()
_, _, _, m := mask.RGBA()
const M = 1<<16 - 1
// The resultant red value is a blend of dstr and srcr, and ranges in [0, M].
// The calculation for green, blue and alpha is similar.
dstr = (dstr*(M-m) + srcr*m) / M
</pre>
<p>
The last line of that code snippet would have been more complicated if we worked
with non-alpha-premultiplied colors, which is why <code>Color</code> uses
alpha-premultiplied values.
</p>
<p>
The image/color package also defines a number of concrete types that implement
the <code>Color</code> interface. For example,
<a href="/pkg/image/color/#RGBA"><code>RGBA</code></a> is a struct that represents
the classic "8 bits per channel" color.
</p>
{{code "/src/pkg/image/color/color.go" `/type RGBA struct/` `/^}/`}}
<p>
Note that the <code>R</code> field of an <code>RGBA</code> is an 8-bit
alpha-premultiplied color in the range [0, 255]. <code>RGBA</code> satisfies the
<code>Color</code> interface by multiplying that value by 0x101 to generate a
16-bit alpha-premultiplied color in the range [0, 65535]. Similarly, the
<a href="/pkg/image/color/#NRGBA"><code>NRGBA</code></a> struct type represents
an 8-bit non-alpha-premultiplied color, as used by the PNG image format. When
manipulating an <code>NRGBA</code>'s fields directly, the values are
non-alpha-premultiplied, but when calling the <code>RGBA</code> method, the
return values are alpha-premultiplied.
</p>
<p>
A <a href="/pkg/image/color/#Model"><code>Model</code></a> is simply
something that can convert <code>Color</code>s to other <code>Color</code>s, possibly lossily. For
example, the <code>GrayModel</code> can convert any <code>Color</code> to a
desaturated <a href="/pkg/image/color/#Gray"><code>Gray</code></a>. A
<code>Palette</code> can convert any <code>Color</code> to one from a
limited palette.
</p>
{{code "/src/pkg/image/color/color.go" `/type Model interface/` `/^}/`}}
{{code "/src/pkg/image/color/color.go" `/type Palette \[\]Color/`}}
<p>
<b>Points and Rectangles</b>
</p>
<p>
A <a href="/pkg/image/#Point"><code>Point</code></a> is an (x, y) co-ordinate
on the integer grid, with axes increasing right and down. It is neither a pixel
nor a grid square. A <code>Point</code> has no intrinsic width, height or
color, but the visualizations below use a small colored square.
</p>
{{code "/src/pkg/image/geom.go" `/type Point struct/` `/^}/`}}
<p>
<img src="image-package-01.png" width="400" height="300">
</p>
{{code "/doc/progs/image_package1.go" `/p := image.Point/`}}
<p>
A <a href="/pkg/image/#Rectangle"><code>Rectangle</code></a> is an axis-aligned
rectangle on the integer grid, defined by its top-left and bottom-right
<code>Point</code>. A <code>Rectangle</code> also has no intrinsic color, but
the visualizations below outline rectangles with a thin colored line, and call
out their <code>Min</code> and <code>Max</code> <code>Point</code>s.
</p>
{{code "/src/pkg/image/geom.go" `/type Rectangle struct/` `/^}/`}}
<p>
For convenience, <code>image.Rect(x0, y0, x1, y1)</code> is equivalent to
<code>image.Rectangle{image.Point{x0, y0}, image.Point{x1, y1}}</code>, but is
much easier to type.
</p>
<p>
A <code>Rectangle</code> is inclusive at the top-left and exclusive at the
bottom-right. For a <code>Point p</code> and a <code>Rectangle r</code>,
<code>p.In(r)</code> if and only if
<code>r.Min.X <= p.X && p.X < r.Max.X</code>, and similarly for <code>Y</code>. This is analagous to how
a slice <code>s[i0:i1]</code> is inclusive at the low end and exclusive at the
high end. (Unlike arrays and slices, a <code>Rectangle</code> often has a
non-zero origin.)
</p>
<p>
<img src="image-package-02.png" width="400" height="300">
</p>
{{code "/doc/progs/image_package2.go" `/r := image.Rect/` `/fmt.Println/`}}
<p>
Adding a <code>Point</code> to a <code>Rectangle</code> translates the
<code>Rectangle</code>. Points and Rectangles are not restricted to be in the
bottom-right quadrant.
</p>
<p>
<img src="image-package-03.png" width="400" height="300">
</p>
{{code "/doc/progs/image_package3.go" `/r := image.Rect/` `/fmt.Println/`}}
<p>
Intersecting two Rectangles yields another Rectangle, which may be empty.
</p>
<p>
<img src="image-package-04.png" width="400" height="300">
</p>
{{code "/doc/progs/image_package4.go" `/r := image.Rect/` `/fmt.Printf/`}}
<p>
Points and Rectangles are passed and returned by value. A function that takes a
<code>Rectangle</code> argument will be as efficient as a function that takes
two <code>Point</code> arguments, or four <code>int</code> arguments.
</p>
<p>
<b>Images</b>
</p>
<p>
An <a href="/pkg/image/#Image">Image</a> maps every grid square in a
<code>Rectangle</code> to a <code>Color</code> from a <code>Model</code>.
"The pixel at (x, y)" refers to the color of the grid square defined by the
points (x, y), (x+1, y), (x+1, y+1) and (x, y+1).
</p>
{{code "/src/pkg/image/image.go" `/type Image interface/` `/^}/`}}
<p>
A common mistake is assuming that an <code>Image</code>'s bounds start at (0,
0). For example, an animated GIF contains a sequence of Images, and each
<code>Image</code> after the first typically only holds pixel data for the area
that changed, and that area doesn't necessarily start at (0, 0). The correct
way to iterate over an <code>Image</code> m's pixels looks like:
</p>
<pre>
b := m.Bounds()
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; y < b.Max.X; x++ {
doStuffWith(m.At(x, y))
}
}
</pre>
<p>
<code>Image</code> implementations do not have to be based on an in-memory
slice of pixel data. For example, a
<a href="/pkg/image/#Uniform"><code>Uniform</code></a> is an
<code>Image</code> of enormous bounds and uniform color, whose in-memory
representation is simply that color.
</p>
{{code "/src/pkg/image/names.go" `/type Uniform struct/` `/^}/`}}
<p>
Typically, though, programs will want an image based on a slice. Struct types
like <a href="/pkg/image/#RGBA"><code>RGBA</code></a> and
<a href="/pkg/image/#Gray"><code>Gray</code></a> (which other packages refer
to as <code>image.RGBA</code> and <code>image.Gray</code>) hold slices of pixel
data and implement the <code>Image</code> interface.
</p>
{{code "/src/pkg/image/image.go" `/type RGBA struct/` `/^}/`}}
<p>
These types also provide a <code>Set(x, y int, c color.Color)</code> method
that allows modifying the image one pixel at a time.
</p>
{{code "/doc/progs/image_package5.go" `/m := image.New/` `/m.Set/`}}
<p>
If you're reading or writing a lot of pixel data, it can be more efficient, but
more complicated, to access these struct type's <code>Pix</code> field directly.
</p>
<p>
The slice-based <code>Image</code> implementations also provide a
<code>SubImage</code> method, which returns an <code>Image</code> backed by the
same array. Modifying the pixels of a sub-image will affect the pixels of the
original image, analagous to how modifying the contents of a sub-slice
<code>s[i0:i1]</code> will affect the contents of the original slice
<code>s</code>.
</p>
<img src="image-package-05.png" width="400" height="300">
{{code "/doc/progs/image_package6.go" `/m0 := image.New/` `/fmt.Println\(m0.Stride/`}}
<p>
For low-level code that works on an image's <code>Pix</code> field, be aware
that ranging over <code>Pix</code> can affect pixels outside an image's bounds.
In the example above, the pixels covered by <code>m1.Pix</code> are shaded in
blue. Higher-level code, such as the <code>At</code> and <code>Set</code>
methods or the <a href="/pkg/image/draw/">image/draw package</a>, will clip
their operations to the image's bounds.
</p>
<p>
<b>Image Formats</b>
</p>
<p>
The standard package library supports a number of common image formats, such as
GIF, JPEG and PNG. If you know the format of a source image file, you can
decode from an <a href="/pkg/io/#Reader"><code>io.Reader</code></a> directly.
</p>
<pre>
import (
"image/jpeg"
"image/png"
"io"
)
// convertJPEGToPNG converts from JPEG to PNG.
func convertJPEGToPNG(w io.Writer, r io.Reader) error {
img, err := jpeg.Decode(r)
if err != nil {
return err
}
return png.Encode(w, img)
}
</pre>
<p>
If you have image data of unknown format, the
<a href="/pkg/image/#Decode"><code>image.Decode</code></a> function can detect
the format. The set of recognized formats is constructed at run time and is not
limited to those in the standard package library. An image format package
typically registers its format in an init function, and the main package will
"underscore import" such a package solely for the side effect of format
registration.
</p>
<pre>
import (
"image"
"image/png"
"io"
_ "code.google.com/p/vp8-go/webp"
_ "image/jpeg"
)
// convertToPNG converts from any recognized format to PNG.
func convertToPNG(w io.Writer, r io.Reader) error {
img, _, err := image.Decode(r)
if err != nil {
return err
}
return png.Encode(w, img)
}
</pre>

View File

@@ -1,7 +0,0 @@
<!--{
"Title": "/doc/articles/"
}-->
<p>
See the <a href="/doc/#articles">Documents page</a> for a complete list of Go articles.
</p>

View File

@@ -1,356 +0,0 @@
<!--{
"Title": "JSON and Go",
"Template": true
}-->
<p>
JSON (JavaScript Object Notation) is a simple data interchange format.
Syntactically it resembles the objects and lists of JavaScript. It is most
commonly used for communication between web back-ends and JavaScript programs
running in the browser, but it is used in many other places, too. Its home page,
<a href="http://json.org">json.org</a>, provides a wonderfully clear and concise
definition of the standard.
</p>
<p>
With the <a href="/pkg/encoding/json/">json package</a> it's a snap to read and
write JSON data from your Go programs.
</p>
<p>
<b>Encoding</b>
</p>
<p>
To encode JSON data we use the
<a href="/pkg/encoding/json/#Marshal"><code>Marshal</code></a> function.
</p>
<pre>
func Marshal(v interface{}) ([]byte, error)
</pre>
<p>
Given the Go data structure, <code>Message</code>,
</p>
{{code "/doc/progs/json1.go" `/type Message/` `/STOP/`}}
<p>
and an instance of <code>Message</code>
</p>
{{code "/doc/progs/json1.go" `/m :=/`}}
<p>
we can marshal a JSON-encoded version of m using <code>json.Marshal</code>:
</p>
{{code "/doc/progs/json1.go" `/b, err :=/`}}
<p>
If all is well, <code>err</code> will be <code>nil</code> and <code>b</code>
will be a <code>[]byte</code> containing this JSON data:
</p>
<pre>
b == []byte(`{"Name":"Alice","Body":"Hello","Time":1294706395881547000}`)
</pre>
<p>
Only data structures that can be represented as valid JSON will be encoded:
</p>
<ul>
<li>
JSON objects only support strings as keys; to encode a Go map type it must be
of the form <code>map[string]T</code> (where <code>T</code> is any Go type
supported by the json package).
</li>
<li>
Channel, complex, and function types cannot be encoded.
</li>
<li>
Cyclic data structures are not supported; they will cause <code>Marshal</code>
to go into an infinite loop.
</li>
<li>
Pointers will be encoded as the values they point to (or 'null' if the pointer
is <code>nil</code>).
</li>
</ul>
<p>
The json package only accesses the exported fields of struct types (those that
begin with an uppercase letter). Therefore only the the exported fields of a
struct will be present in the JSON output.
</p>
<p>
<b>Decoding</b>
</p>
<p>
To decode JSON data we use the
<a href="/pkg/encoding/json/#Unmarshal"><code>Unmarshal</code></a> function.
</p>
<pre>
func Unmarshal(data []byte, v interface{}) error
</pre>
<p>
We must first create a place where the decoded data will be stored
</p>
{{code "/doc/progs/json1.go" `/var m Message/`}}
<p>
and call <code>json.Unmarshal</code>, passing it a <code>[]byte</code> of JSON
data and a pointer to <code>m</code>
</p>
{{code "/doc/progs/json1.go" `/err := json.Unmarshal/`}}
<p>
If <code>b</code> contains valid JSON that fits in <code>m</code>, after the
call <code>err</code> will be <code>nil</code> and the data from <code>b</code>
will have been stored in the struct <code>m</code>, as if by an assignment
like:
</p>
{{code "/doc/progs/json1.go" `/m = Message/` `/STOP/`}}
<p>
How does <code>Unmarshal</code> identify the fields in which to store the
decoded data? For a given JSON key <code>"Foo"</code>, <code>Unmarshal</code>
will look through the destination struct's fields to find (in order of
preference):
</p>
<ul>
<li>
An exported field with a tag of <code>"Foo"</code> (see the
<a href="/ref/spec#Struct_types">Go spec</a> for more on struct tags),
</li>
<li>
An exported field named <code>"Foo"</code>, or
</li>
<li>
An exported field named <code>"FOO"</code> or <code>"FoO"</code> or some other
case-insensitive match of <code>"Foo"</code>.
</li>
</ul>
<p>
What happens when the structure of the JSON data doesn't exactly match the Go
type?
</p>
{{code "/doc/progs/json1.go" `/"Food":"Pickle"/` `/STOP/`}}
<p>
<code>Unmarshal</code> will decode only the fields that it can find in the
destination type. In this case, only the Name field of m will be populated,
and the Food field will be ignored. This behavior is particularly useful when
you wish to pick only a few specific fields out of a large JSON blob. It also
means that any unexported fields in the destination struct will be unaffected
by <code>Unmarshal</code>.
</p>
<p>
But what if you don't know the structure of your JSON data beforehand?
</p>
<p>
<b>Generic JSON with interface{}</b>
</p>
<p>
The <code>interface{}</code> (empty interface) type describes an interface with
zero methods. Every Go type implements at least zero methods and therefore
satisfies the empty interface.
</p>
<p>
The empty interface serves as a general container type:
</p>
{{code "/doc/progs/json2.go" `/var i interface{}/` `/STOP/`}}
<p>
A type assertion accesses the underlying concrete type:
</p>
{{code "/doc/progs/json2.go" `/r := i/` `/STOP/`}}
<p>
Or, if the underlying type is unknown, a type switch determines the type:
</p>
{{code "/doc/progs/json2.go" `/switch v/` `/STOP/`}}
The json package uses <code>map[string]interface{}</code> and
<code>[]interface{}</code> values to store arbitrary JSON objects and arrays;
it will happily unmarshal any valid JSON blob into a plain
<code>interface{}</code> value. The default concrete Go types are:
<ul>
<li>
<code>bool</code> for JSON booleans,
</li>
<li>
<code>float64</code> for JSON numbers,
</li>
<li>
<code>string</code> for JSON strings, and
</li>
<li>
<code>nil</code> for JSON null.
</li>
</ul>
<p>
<b>Decoding arbitrary data</b>
</p>
<p>
Consider this JSON data, stored in the variable <code>b</code>:
</p>
{{code "/doc/progs/json3.go" `/b :=/`}}
<p>
Without knowing this data's structure, we can decode it into an
<code>interface{}</code> value with <code>Unmarshal</code>:
</p>
{{code "/doc/progs/json3.go" `/var f interface/` `/STOP/`}}
<p>
At this point the Go value in <code>f</code> would be a map whose keys are
strings and whose values are themselves stored as empty interface values:
</p>
{{code "/doc/progs/json3.go" `/f = map/` `/STOP/`}}
<p>
To access this data we can use a type assertion to access <code>f</code>'s
underlying <code>map[string]interface{}</code>:
</p>
{{code "/doc/progs/json3.go" `/m := f/`}}
<p>
We can then iterate through the map with a range statement and use a type switch
to access its values as their concrete types:
</p>
{{code "/doc/progs/json3.go" `/for k, v/` `/STOP/`}}
<p>
In this way you can work with unknown JSON data while still enjoying the
benefits of type safety.
</p>
<p>
<b>Reference Types</b>
</p>
<p>
Let's define a Go type to contain the data from the previous example:
</p>
{{code "/doc/progs/json4.go" `/type FamilyMember/` `/STOP/`}}
{{code "/doc/progs/json4.go" `/var m FamilyMember/` `/STOP/`}}
<p>
Unmarshaling that data into a <code>FamilyMember</code> value works as
expected, but if we look closely we can see a remarkable thing has happened.
With the var statement we allocated a <code>FamilyMember</code> struct, and
then provided a pointer to that value to <code>Unmarshal</code>, but at that
time the <code>Parents</code> field was a <code>nil</code> slice value. To
populate the <code>Parents</code> field, <code>Unmarshal</code> allocated a new
slice behind the scenes. This is typical of how <code>Unmarshal</code> works
with the supported reference types (pointers, slices, and maps).
</p>
<p>
Consider unmarshaling into this data structure:
</p>
<pre>
type Foo struct {
Bar *Bar
}
</pre>
<p>
If there were a <code>Bar</code> field in the JSON object,
<code>Unmarshal</code> would allocate a new <code>Bar</code> and populate it.
If not, <code>Bar</code> would be left as a <code>nil</code> pointer.
</p>
<p>
From this a useful pattern arises: if you have an application that receives a
few distinct message types, you might define "receiver" structure like
</p>
<pre>
type IncomingMessage struct {
Cmd *Command
Msg *Message
}
</pre>
<p>
and the sending party can populate the <code>Cmd</code> field and/or the
<code>Msg</code> field of the top-level JSON object, depending on the type of
message they want to communicate. <code>Unmarshal</code>, when decoding the
JSON into an <code>IncomingMessage</code> struct, will only allocate the data
structures present in the JSON data. To know which messages to process, the
programmer need simply test that either <code>Cmd</code> or <code>Msg</code> is
not <code>nil</code>.
</p>
<p>
<b>Streaming Encoders and Decoders</b>
</p>
<p>
The json package provides <code>Decoder</code> and <code>Encoder</code> types
to support the common operation of reading and writing streams of JSON data.
The <code>NewDecoder</code> and <code>NewEncoder</code> functions wrap the
<a href="/pkg/io/#Reader"><code>io.Reader</code></a> and
<a href="/pkg/io/#Writer"><code>io.Writer</code></a> interface types.
</p>
<pre>
func NewDecoder(r io.Reader) *Decoder
func NewEncoder(w io.Writer) *Encoder
</pre>
<p>
Here's an example program that reads a series of JSON objects from standard
input, removes all but the <code>Name</code> field from each object, and then
writes the objects to standard output:
</p>
{{code "/doc/progs/json5.go" `/package main/` `$`}}
<p>
Due to the ubiquity of Readers and Writers, these <code>Encoder</code> and
<code>Decoder</code> types can be used in a broad range of scenarios, such as
reading and writing to HTTP connections, WebSockets, or files.
</p>
<p>
<b>References</b>
</p>
<p>
For more information see the <a href="/pkg/encoding/json/">json package documentation</a>. For an example usage of
json see the source files of the <a href="/pkg/net/rpc/jsonrpc/">jsonrpc package</a>.
</p>

View File

@@ -1,78 +0,0 @@
<!--{
"Title": "JSON-RPC: a tale of interfaces"
}-->
<p>
Here we present an example where Go's
<a href="/doc/effective_go.html#interfaces_and_types">interfaces</a> made it
easy to refactor some existing code to make it more flexible and extensible.
Originally, the standard library's <a href="/pkg/net/rpc/">RPC package</a> used
a custom wire format called <a href="/pkg/encoding/gob/">gob</a>. For a
particular application, we wanted to use <a href="/pkg/encoding/json/">JSON</a>
as an alternate wire format.
</p>
<p>
We first defined a pair of interfaces to describe the functionality of the
existing wire format, one for the client, and one for the server (depicted
below).
</p>
<pre>
type ServerCodec interface {
ReadRequestHeader(*Request) error
ReadRequestBody(interface{}) error
WriteResponse(*Response, interface{}) error
Close() error
}
</pre>
<p>
On the server side, we then changed two internal function signatures to accept
the <code>ServerCodec</code> interface instead of our existing
<code>gob.Encoder</code>. Here's one of them:
</p>
<pre>
func sendResponse(sending *sync.Mutex, req *Request,
reply interface{}, enc *gob.Encoder, errmsg string)
</pre>
<p>
became
</p>
<pre>
func sendResponse(sending *sync.Mutex, req *Request,
reply interface{}, enc ServerCodec, errmsg string)
</pre>
<p>
We then wrote a trivial <code>gobServerCodec</code> wrapper to reproduce the
original functionality. From there it is simple to build a
<code>jsonServerCodec</code>.
</p>
<p>
After some similar changes to the client side, this was the full extent of the
work we needed to do on the RPC package. This whole exercise took about 20
minutes! After tidying up and testing the new code, the
<a href="http://code.google.com/p/go/source/diff?spec=svn9daf796ebf1cae97b2fcf760a4ab682f1f063f29&r=9daf796ebf1cae97b2fcf760a4ab682f1f063f29&format=side&path=/src/pkg/rpc/server.go">final changeset</a>
was submitted.
</p>
<p>
In an inheritance-oriented language like Java or C++, the obvious path would be
to generalize the RPC class, and create JsonRPC and GobRPC subclasses. However,
this approach becomes tricky if you want to make a further generalization
orthogonal to that hierarchy. (For example, if you were to implement an
alternate RPC standard). In our Go package, we took a route that is both
conceptually simpler and requires less code be written or changed.
</p>
<p>
A vital quality for any codebase is maintainability. As needs change, it is
essential to adapt your code easily and cleanly, lest it become unwieldy to work
with. We believe Go's lightweight, composition-oriented type system provides a
means of structuring code that scales.
</p>

View File

@@ -1,649 +0,0 @@
<!--{
"Title": "The Laws of Reflection",
"Template": true
}-->
<p>
Reflection in computing is the
ability of a program to examine its own structure, particularly
through types; it's a form of metaprogramming. It's also a great
source of confusion.
</p>
<p>
In this article we attempt to clarify things by explaining how
reflection works in Go. Each language's reflection model is
different (and many languages don't support it at all), but
this article is about Go, so for the rest of this article the word
"reflection" should be taken to mean "reflection in Go".
</p>
<p><b>Types and interfaces</b></p>
<p>
Because reflection builds on the type system, let's start with a
refresher about types in Go.
</p>
<p>
Go is statically typed. Every variable has a static type, that is,
exactly one type known and fixed at compile time: <code>int</code>,
<code>float32</code>, <code>*MyType</code>, <code>[]byte</code>,
and so on. If we declare
</p>
{{code "/doc/progs/interface.go" `/type MyInt/` `/STOP/`}}
<p>
then <code>i</code> has type <code>int</code> and <code>j</code>
has type <code>MyInt</code>. The variables <code>i</code> and
<code>j</code> have distinct static types and, although they have
the same underlying type, they cannot be assigned to one another
without a conversion.
</p>
<p>
One important category of type is interface types, which represent
fixed sets of methods. An interface variable can store any concrete
(non-interface) value as long as that value implements the
interface's methods. A well-known pair of examples is
<code>io.Reader</code> and <code>io.Writer</code>, the types
<code>Reader</code> and <code>Writer</code> from the
<a href="/pkg/io/">io package</a>:
</p>
{{code "/doc/progs/interface.go" `/// Reader/` `/STOP/`}}
<p>
Any type that implements a <code>Read</code> (or
<code>Write</code>) method with this signature is said to implement
<code>io.Reader</code> (or <code>io.Writer</code>). For the
purposes of this discussion, that means that a variable of type
<code>io.Reader</code> can hold any value whose type has a
<code>Read</code> method:
</p>
{{code "/doc/progs/interface.go" `/func readers/` `/STOP/`}}
<p>
It's important to be clear that whatever concrete value
<code>r</code> may hold, <code>r</code>'s type is always
<code>io.Reader</code>: Go is statically typed and the static type
of <code>r</code> is <code>io.Reader</code>.</p>
<p>
An extremely important example of an interface type is the empty
interface:
</p>
<pre>
interface{}
</pre>
<p>
It represents the empty set of methods and is satisfied by any
value at all, since any value has zero or more methods.
</p>
<p>
Some people say that Go's interfaces are dynamically typed, but
that is misleading. They are statically typed: a variable of
interface type always has the same static type, and even though at
run time the value stored in the interface variable may change
type, that value will always satisfy the interface.
</p>
<p>
We need to be precise about all this because reflection and
interfaces are closely related.
</p>
<p><b>The representation of an interface</b></p>
<p>
Russ Cox has written a
<a href="http://research.swtch.com/2009/12/go-data-structures-interfaces.html">detailed blog post</a>
about the representation of interface values in Go. It's not necessary to
repeat the full story here, but a simplified summary is in order.
</p>
<p>
A variable of interface type stores a pair: the concrete value
assigned to the variable, and that value's type descriptor.
To be more precise, the value is the underlying concrete data item
that implements the interface and the type describes the full type
of that item. For instance, after
</p>
{{code "/doc/progs/interface.go" `/func typeAssertions/` `/STOP/`}}
<p>
<code>r</code> contains, schematically, the (value, type) pair,
(<code>tty</code>, <code>*os.File</code>). Notice that the type
<code>*os.File</code> implements methods other than
<code>Read</code>; even though the interface value provides access
only to the <code>Read</code> method, the value inside carries all
the type information about that value. That's why we can do things
like this:
</p>
{{code "/doc/progs/interface.go" `/var w io.Writer/` `/STOP/`}}
<p>
The expression in this assignment is a type assertion; what it
asserts is that the item inside <code>r</code> also implements
<code>io.Writer</code>, and so we can assign it to <code>w</code>.
After the assignment, <code>w</code> will contain the pair
(<code>tty</code>, <code>*os.File</code>). That's the same pair as
was held in <code>r</code>. The static type of the interface
determines what methods may be invoked with an interface variable,
even though the concrete value inside may have a larger set of
methods.
</p>
<p>
Continuing, we can do this:
</p>
{{code "/doc/progs/interface.go" `/var empty interface{}/` `/STOP/`}}
<p>
and our empty interface value <code>e</code> will again contain
that same pair, (<code>tty</code>, <code>*os.File</code>). That's
handy: an empty interface can hold any value and contains all the
information we could ever need about that value.
</p>
<p>
(We don't need a type assertion here because it's known statically
that <code>w</code> satisfies the empty interface. In the example
where we moved a value from a <code>Reader</code> to a
<code>Writer</code>, we needed to be explicit and use a type
assertion because <code>Writer</code>'s methods are not a
subset of <code>Reader</code>'s.)
</p>
<p>
One important detail is that the pair inside an interface always
has the form (value, concrete type) and cannot have the form
(value, interface type). Interfaces do not hold interface
values.
</p>
<p>
Now we're ready to reflect.
</p>
<p><b>The first law of reflection</b></p>
<p><b>1. Reflection goes from interface value to reflection object.</b></p>
<p>
At the basic level, reflection is just a mechanism to examine the
type and value pair stored inside an interface variable. To get
started, there are two types we need to know about in
<a href="/pkg/reflect/">package reflect</a>:
<a href="/pkg/reflect/#Type">Type</a> and
<a href="/pkg/reflect/#Value">Value</a>. Those two types
give access to the contents of an interface variable, and two
simple functions, called <code>reflect.TypeOf</code> and
<code>reflect.ValueOf</code>, retrieve <code>reflect.Type</code>
and <code>reflect.Value</code> pieces out of an interface value.
(Also, from the <code>reflect.Value</code> it's easy to get
to the <code>reflect.Type</code>, but let's keep the
<code>Value</code> and <code>Type</code> concepts separate for
now.)
</p>
<p>
Let's start with <code>TypeOf</code>:
</p>
{{code "/doc/progs/interface2.go" `/package main/` `/STOP main/`}}
<p>
This program prints
</p>
<pre>
type: float64
</pre>
<p>
You might be wondering where the interface is here, since the program looks
like it's passing the <code>float64</code> variable <code>x</code>, not an
interface value, to <code>reflect.TypeOf</code>. But it's there; as
<a href="/pkg/reflect/#Type.TypeOf">godoc reports</a>, the signature of
<code>reflect.TypeOf</code> includes an empty interface:
</p>
<pre>
// TypeOf returns the reflection Type of the value in the interface{}.
func TypeOf(i interface{}) Type
</pre>
<p>
When we call <code>reflect.TypeOf(x)</code>, <code>x</code> is
first stored in an empty interface, which is then passed as the
argument; <code>reflect.TypeOf</code> unpacks that empty interface
to recover the type information.
</p>
<p>
The <code>reflect.ValueOf</code> function, of course, recovers the
value (from here on we'll elide the boilerplate and focus just on
the executable code):
</p>
{{code "/doc/progs/interface2.go" `/START f9/` `/STOP/`}}
<p>
prints
</p>
<pre>
value: &lt;float64 Value&gt;
</pre>
<p>
Both <code>reflect.Type</code> and <code>reflect.Value</code> have
lots of methods to let us examine and manipulate them. One
important example is that <code>Value</code> has a
<code>Type</code> method that returns the <code>Type</code> of a
<code>reflect.Value</code>. Another is that both <code>Type</code>
and <code>Value</code> have a <code>Kind</code> method that returns
a constant indicating what sort of item is stored:
<code>Uint</code>, <code>Float64</code>, <code>Slice</code>, and so
on. Also methods on <code>Value</code> with names like
<code>Int</code> and <code>Float</code> let us grab values (as
<code>int64</code> and <code>float64</code>) stored inside:
</p>
{{code "/doc/progs/interface2.go" `/START f1/` `/STOP/`}}
<p>
prints
</p>
<pre>
type: float64
kind is float64: true
value: 3.4
</pre>
<p>
There are also methods like <code>SetInt</code> and
<code>SetFloat</code> but to use them we need to understand
settability, the subject of the third law of reflection, discussed
below.
</p>
<p>
The reflection library has a couple of properties worth singling
out. First, to keep the API simple, the "getter" and "setter"
methods of <code>Value</code> operate on the largest type that can
hold the value: <code>int64</code> for all the signed integers, for
instance. That is, the <code>Int</code> method of
<code>Value</code> returns an <code>int64</code> and the
<code>SetInt</code> value takes an <code>int64</code>; it may be
necessary to convert to the actual type involved:
</p>
{{code "/doc/progs/interface2.go" `/START f2/` `/STOP/`}}
<p>
The second property is that the <code>Kind</code> of a reflection
object describes the underlying type, not the static type. If a
reflection object contains a value of a user-defined integer type,
as in
</p>
{{code "/doc/progs/interface2.go" `/START f3/` `/STOP/`}}
<p>
the <code>Kind</code> of <code>v</code> is still
<code>reflect.Int</code>, even though the static type of
<code>x</code> is <code>MyInt</code>, not <code>int</code>. In
other words, the <code>Kind</code> cannot discriminate an int from
a <code>MyInt</code> even though the <code>Type</code> can.
</p>
<p><b>The second law of reflection</b></p>
<p><b>2. Reflection goes from reflection object to interface
value.</b></p>
<p>
Like physical reflection, reflection in Go generates its own
inverse.
</p>
<p>
Given a <code>reflect.Value</code> we can recover an interface
value using the <code>Interface</code> method; in effect the method
packs the type and value information back into an interface
representation and returns the result:
</p>
<pre>
// Interface returns v's value as an interface{}.
func (v Value) Interface() interface{}
</pre>
<p>
As a consequence we can say
</p>
{{code "/doc/progs/interface2.go" `/START f3b/` `/STOP/`}}
<p>
to print the <code>float64</code> value represented by the
reflection object <code>v</code>.
</p>
<p>
We can do even better, though. The arguments to
<code>fmt.Println</code>, <code>fmt.Printf</code> and so on are all
passed as empty interface values, which are then unpacked by the
<code>fmt</code> package internally just as we have been doing in
the previous examples. Therefore all it takes to print the contents
of a <code>reflect.Value</code> correctly is to pass the result of
the <code>Interface</code> method to the formatted print
routine:
</p>
{{code "/doc/progs/interface2.go" `/START f3c/` `/STOP/`}}
<p>
(Why not <code>fmt.Println(v)</code>? Because <code>v</code> is a
<code>reflect.Value</code>; we want the concrete value it holds.)
Since our value is a <code>float64</code>, we can even use a
floating-point format if we want:
</p>
{{code "/doc/progs/interface2.go" `/START f3d/` `/STOP/`}}
<p>
and get in this case
</p>
<pre>
3.4e+00
</pre>
<p>
Again, there's no need to type-assert the result of
<code>v.Interface()</code> to <code>float64</code>; the empty
interface value has the concrete value's type information inside
and <code>Printf</code> will recover it.
</p>
<p>
In short, the <code>Interface</code> method is the inverse of the
<code>ValueOf</code> function, except that its result is always of
static type <code>interface{}</code>.
</p>
<p>
Reiterating: Reflection goes from interface values to reflection
objects and back again.
</p>
<p><b>The third law of reflection</b></p>
<p><b>3. To modify a reflection object, the value must be settable.</b></p>
<p>
The third law is the most subtle and confusing, but it's easy
enough to understand if we start from first principles.
</p>
<p>
Here is some code that does not work, but is worth studying.
</p>
{{code "/doc/progs/interface2.go" `/START f4/` `/STOP/`}}
<p>
If you run this code, it will panic with the cryptic message
</p>
<pre>
panic: reflect.Value.SetFloat using unaddressable value
</pre>
<p>
The problem is not that the value <code>7.1</code> is not
addressable; it's that <code>v</code> is not settable. Settability
is a property of a reflection <code>Value</code>, and not all
reflection <code>Values</code> have it.
</p>
<p>
The <code>CanSet</code> method of <code>Value</code> reports the
settability of a <code>Value</code>; in our case,
</p>
{{code "/doc/progs/interface2.go" `/START f5/` `/STOP/`}}
<p>
prints
</p>
<pre>
settability of v: false
</pre>
<p>
It is an error to call a <code>Set</code> method on an non-settable
<code>Value</code>. But what is settability?
</p>
<p>
Settability is a bit like addressability, but stricter. It's the
property that a reflection object can modify the actual storage
that was used to create the reflection object. Settability is
determined by whether the reflection object holds the original
item. When we say
</p>
{{code "/doc/progs/interface2.go" `/START f6/` `/STOP/`}}
<p>
we pass a <em>copy</em> of <code>x</code> to
<code>reflect.ValueOf</code>, so the interface value created as the
argument to <code>reflect.ValueOf</code> is a <em>copy</em> of
<code>x</code>, not <code>x</code> itself. Thus, if the
statement
</p>
{{code "/doc/progs/interface2.go" `/START f6b/` `/STOP/`}}
<p>
were allowed to succeed, it would not update <code>x</code>, even
though <code>v</code> looks like it was created from
<code>x</code>. Instead, it would update the copy of <code>x</code>
stored inside the reflection value and <code>x</code> itself would
be unaffected. That would be confusing and useless, so it is
illegal, and settability is the property used to avoid this
issue.
</p>
<p>
If this seems bizarre, it's not. It's actually a familiar situation
in unusual garb. Think of passing <code>x</code> to a
function:
</p>
<pre>
f(x)
</pre>
<p>
We would not expect <code>f</code> to be able to modify
<code>x</code> because we passed a copy of <code>x</code>'s value,
not <code>x</code> itself. If we want <code>f</code> to modify
<code>x</code> directly we must pass our function the address of
<code>x</code> (that is, a pointer to <code>x</code>):</p>
<p>
<code>f(&amp;x)</code>
</p>
<p>
This is straightforward and familiar, and reflection works the same
way. If we want to modify <code>x</code> by reflection, we must
give the reflection library a pointer to the value we want to
modify.
</p>
<p>
Let's do that. First we initialize <code>x</code> as usual
and then create a reflection value that points to it, called
<code>p</code>.
</p>
{{code "/doc/progs/interface2.go" `/START f7/` `/STOP/`}}
<p>
The output so far is
</p>
<pre>
type of p: *float64
settability of p: false
</pre>
<p>
The reflection object <code>p</code> isn't settable, but it's not
<code>p</code> we want to set, it's (in effect) <code>*p</code>. To
get to what <code>p</code> points to, we call the <code>Elem</code>
method of <code>Value</code>, which indirects through the pointer,
and save the result in a reflection <code>Value</code> called
<code>v</code>:
</p>
{{code "/doc/progs/interface2.go" `/START f7b/` `/STOP/`}}
<p>
Now <code>v</code> is a settable reflection object, as the output
demonstrates,
</p>
<pre>
settability of v: true
</pre>
<p>
and since it represents <code>x</code>, we are finally able to use
<code>v.SetFloat</code> to modify the value of
<code>x</code>:
</p>
{{code "/doc/progs/interface2.go" `/START f7c/` `/STOP/`}}
<p>
The output, as expected, is
</p>
<pre>
7.1
7.1
</pre>
<p>
Reflection can be hard to understand but it's doing exactly what
the language does, albeit through reflection <code>Types</code> and
<code>Values</code> that can disguise what's going on. Just keep in
mind that reflection Values need the address of something in order
to modify what they represent.
</p>
<p><b>Structs</b></p>
<p>
In our previous example <code>v</code> wasn't a pointer itself, it
was just derived from one. A common way for this situation to arise
is when using reflection to modify the fields of a structure. As
long as we have the address of the structure, we can modify its
fields.
</p>
<p>
Here's a simple example that analyzes a struct value, <code>t</code>. We create
the reflection object with the address of the struct because we'll want to
modify it later. Then we set <code>typeOfT</code> to its type and iterate over
the fields using straightforward method calls
(see <a href="/pkg/reflect/">package reflect</a> for details).
Note that we extract the names of the fields from the struct type, but the
fields themselves are regular <code>reflect.Value</code> objects.
</p>
{{code "/doc/progs/interface2.go" `/START f8/` `/STOP/`}}
<p>
The output of this program is
</p>
<pre>
0: A int = 23
1: B string = skidoo
</pre>
<p>
There's one more point about settability introduced in
passing here: the field names of <code>T</code> are upper case
(exported) because only exported fields of a struct are
settable.
</p>
<p>
Because <code>s</code> contains a settable reflection object, we
can modify the fields of the structure.
</p>
{{code "/doc/progs/interface2.go" `/START f8b/` `/STOP/`}}
<p>
And here's the result:
</p>
<pre>
t is now {77 Sunset Strip}
</pre>
<p>
If we modified the program so that <code>s</code> was created from
<code>t</code>, not <code>&amp;t</code>, the calls to
<code>SetInt</code> and <code>SetString</code> would fail as the
fields of <code>t</code> would not be settable.
</p>
<p><b>Conclusion</b></p>
<p>
Here again are the laws of reflection:
</p>
<ol>
<li>Reflection goes from interface value to reflection
object.</li>
<li>Reflection goes from reflection object to interface
value.</li>
<li>To modify a reflection object, the value must be settable.</li>
</ol>
<p>
Once you understand these laws reflection in Go becomes much easier
to use, although it remains subtle. It's a powerful tool that
should be used with care and avoided unless strictly
necessary.
</p>
<p>
There's plenty more to reflection that we haven't covered &mdash;
sending and receiving on channels, allocating memory, using slices
and maps, calling methods and functions &mdash; but this post is
long enough. We'll cover some of those topics in a later
article.
</p>

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@@ -1,438 +0,0 @@
<!--{
"Title": "Slices: usage and internals",
"Template": true
}-->
<p>
Go's slice type provides a convenient and efficient means of working with
sequences of typed data. Slices are analogous to arrays in other languages, but
have some unusual properties. This article will look at what slices are and how
they are used.
</p>
<p>
<b>Arrays</b>
</p>
<p>
The slice type is an abstraction built on top of Go's array type, and so to
understand slices we must first understand arrays.
</p>
<p>
An array type definition specifies a length and an element type. For example,
the type <code>[4]int</code> represents an array of four integers. An array's
size is fixed; its length is part of its type (<code>[4]int</code> and
<code>[5]int</code> are distinct, incompatible types). Arrays can be indexed in
the usual way, so the expression <code>s[n]</code> accesses the <i>n</i>th
element:
</p>
<pre>
var a [4]int
a[0] = 1
i := a[0]
// i == 1
</pre>
<p>
Arrays do not need to be initialized explicitly; the zero value of an array is
a ready-to-use array whose elements are themselves zeroed:
</p>
<pre>
// a[2] == 0, the zero value of the int type
</pre>
<p>
The in-memory representation of <code>[4]int</code> is just four integer values laid out sequentially:
</p>
<p>
<img src="slice-array.png">
</p>
<p>
Go's arrays are values. An array variable denotes the entire array; it is not a
pointer to the first array element (as would be the case in C). This means
that when you assign or pass around an array value you will make a copy of its
contents. (To avoid the copy you could pass a <i>pointer</i> to the array, but
then that's a pointer to an array, not an array.) One way to think about arrays
is as a sort of struct but with indexed rather than named fields: a fixed-size
composite value.
</p>
<p>
An array literal can be specified like so:
</p>
<pre>
b := [2]string{"Penn", "Teller"}
</pre>
<p>
Or, you can have the compiler count the array elements for you:
</p>
<pre>
b := [...]string{"Penn", "Teller"}
</pre>
<p>
In both cases, the type of <code>b</code> is <code>[2]string</code>.
</p>
<p>
<b>Slices</b>
</p>
<p>
Arrays have their place, but they're a bit inflexible, so you don't see them
too often in Go code. Slices, though, are everywhere. They build on arrays to
provide great power and convenience.
</p>
<p>
The type specification for a slice is <code>[]T</code>, where <code>T</code> is
the type of the elements of the slice. Unlike an array type, a slice type has
no specified length.
</p>
<p>
A slice literal is declared just like an array literal, except you leave out
the element count:
</p>
<pre>
letters := []string{"a", "b", "c", "d"}
</pre>
<p>
A slice can be created with the built-in function called <code>make</code>,
which has the signature,
</p>
<pre>
func make([]T, len, cap) []T
</pre>
<p>
where T stands for the element type of the slice to be created. The
<code>make</code> function takes a type, a length, and an optional capacity.
When called, <code>make</code> allocates an array and returns a slice that
refers to that array.
</p>
<pre>
var s []byte
s = make([]byte, 5, 5)
// s == []byte{0, 0, 0, 0, 0}
</pre>
<p>
When the capacity argument is omitted, it defaults to the specified length.
Here's a more succinct version of the same code:
</p>
<pre>
s := make([]byte, 5)
</pre>
<p>
The length and capacity of a slice can be inspected using the built-in
<code>len</code> and <code>cap</code> functions.
</p>
<pre>
len(s) == 5
cap(s) == 5
</pre>
<p>
The next two sections discuss the relationship between length and capacity.
</p>
<p>
The zero value of a slice is <code>nil</code>. The <code>len</code> and
<code>cap</code> functions will both return 0 for a nil slice.
</p>
<p>
A slice can also be formed by "slicing" an existing slice or array. Slicing is
done by specifying a half-open range with two indices separated by a colon. For
example, the expression <code>b[1:4]</code> creates a slice including elements
1 through 3 of <code>b</code> (the indices of the resulting slice will be 0
through 2).
</p>
<pre>
b := []byte{'g', 'o', 'l', 'a', 'n', 'g'}
// b[1:4] == []byte{'o', 'l', 'a'}, sharing the same storage as b
</pre>
<p>
The start and end indices of a slice expression are optional; they default to zero and the slice's length respectively:
</p>
<pre>
// b[:2] == []byte{'g', 'o'}
// b[2:] == []byte{'l', 'a', 'n', 'g'}
// b[:] == b
</pre>
<p>
This is also the syntax to create a slice given an array:
</p>
<pre>
x := [3]string{"Лайка", "Белка", "Стрелка"}
s := x[:] // a slice referencing the storage of x
</pre>
<p>
<b>Slice internals</b>
</p>
<p>
A slice is a descriptor of an array segment. It consists of a pointer to the
array, the length of the segment, and its capacity (the maximum length of the
segment).
</p>
<p>
<img src="slice-struct.png">
</p>
<p>
Our variable <code>s</code>, created earlier by <code>make([]byte, 5)</code>,
is structured like this:
</p>
<p>
<img src="slice-1.png">
</p>
<p>
The length is the number of elements referred to by the slice. The capacity is
the number of elements in the underlying array (beginning at the element
referred to by the slice pointer). The distinction between length and capacity
will be made clear as we walk through the next few examples.
</p>
<p>
As we slice <code>s</code>, observe the changes in the slice data structure and
their relation to the underlying array:
</p>
<pre>
s = s[2:4]
</pre>
<p>
<img src="slice-2.png">
</p>
<p>
Slicing does not copy the slice's data. It creates a new slice value that
points to the original array. This makes slice operations as efficient as
manipulating array indices. Therefore, modifying the <i>elements</i> (not the
slice itself) of a re-slice modifies the elements of the original slice:
</p>
<pre>
d := []byte{'r', 'o', 'a', 'd'}
e := d[2:]
// e == []byte{'a', 'd'}
e[1] == 'm'
// e == []byte{'a', 'm'}
// d == []byte{'r', 'o', 'a', 'm'}
</pre>
<p>
Earlier we sliced <code>s</code> to a length shorter than its capacity. We can
grow s to its capacity by slicing it again:
</p>
<pre>
s = s[:cap(s)]
</pre>
<p>
<img src="slice-3.png">
</p>
<p>
A slice cannot be grown beyond its capacity. Attempting to do so will cause a
runtime panic, just as when indexing outside the bounds of a slice or array.
Similarly, slices cannot be re-sliced below zero to access earlier elements in
the array.
</p>
<p>
<b>Growing slices (the copy and append functions)</b>
</p>
<p>
To increase the capacity of a slice one must create a new, larger slice and
copy the contents of the original slice into it. This technique is how dynamic
array implementations from other languages work behind the scenes. The next
example doubles the capacity of <code>s</code> by making a new slice,
<code>t</code>, copying the contents of <code>s</code> into <code>t</code>, and
then assigning the slice value <code>t</code> to <code>s</code>:
</p>
<pre>
t := make([]byte, len(s), (cap(s)+1)*2) // +1 in case cap(s) == 0
for i := range s {
t[i] = s[i]
}
s = t
</pre>
<p>
The looping piece of this common operation is made easier by the built-in copy
function. As the name suggests, copy copies data from a source slice to a
destination slice. It returns the number of elements copied.
</p>
<pre>
func copy(dst, src []T) int
</pre>
<p>
The <code>copy</code> function supports copying between slices of different
lengths (it will copy only up to the smaller number of elements). In addition,
<code>copy</code> can handle source and destination slices that share the same
underlying array, handling overlapping slices correctly.
</p>
<p>
Using <code>copy</code>, we can simplify the code snippet above:
</p>
<pre>
t := make([]byte, len(s), (cap(s)+1)*2)
copy(t, s)
s = t
</pre>
<p>
A common operation is to append data to the end of a slice. This function
appends byte elements to a slice of bytes, growing the slice if necessary, and
returns the updated slice value:
</p>
{{code "/doc/progs/slices.go" `/AppendByte/` `/STOP/`}}
<p>
One could use <code>AppendByte</code> like this:
</p>
<pre>
p := []byte{2, 3, 5}
p = AppendByte(p, 7, 11, 13)
// p == []byte{2, 3, 5, 7, 11, 13}
</pre>
<p>
Functions like <code>AppendByte</code> are useful because they offer complete
control over the way the slice is grown. Depending on the characteristics of
the program, it may be desirable to allocate in smaller or larger chunks, or to
put a ceiling on the size of a reallocation.
</p>
<p>
But most programs don't need complete control, so Go provides a built-in
<code>append</code> function that's good for most purposes; it has the
signature
</p>
<pre>
func append(s []T, x ...T) []T
</pre>
<p>
The <code>append</code> function appends the elements <code>x</code> to the end
of the slice <code>s</code>, and grows the slice if a greater capacity is
needed.
</p>
<pre>
a := make([]int, 1)
// a == []int{0}
a = append(a, 1, 2, 3)
// a == []int{0, 1, 2, 3}
</pre>
<p>
To append one slice to another, use <code>...</code> to expand the second
argument to a list of arguments.
</p>
<pre>
a := []string{"John", "Paul"}
b := []string{"George", "Ringo", "Pete"}
a = append(a, b...) // equivalent to "append(a, b[0], b[1], b[2])"
// a == []string{"John", "Paul", "George", "Ringo", "Pete"}
</pre>
<p>
Since the zero value of a slice (<code>nil</code>) acts like a zero-length
slice, you can declare a slice variable and then append to it in a loop:
</p>
{{code "/doc/progs/slices.go" `/Filter/` `/STOP/`}}
<p>
<b>A possible "gotcha"</b>
</p>
<p>
As mentioned earlier, re-slicing a slice doesn't make a copy of the underlying
array. The full array will be kept in memory until it is no longer referenced.
Occasionally this can cause the program to hold all the data in memory when
only a small piece of it is needed.
</p>
<p>
For example, this <code>FindDigits</code> function loads a file into memory and
searches it for the first group of consecutive numeric digits, returning them
as a new slice.
</p>
{{code "/doc/progs/slices.go" `/digit/` `/STOP/`}}
<p>
This code behaves as advertised, but the returned <code>[]byte</code> points
into an array containing the entire file. Since the slice references the
original array, as long as the slice is kept around the garbage collector can't
release the array; the few useful bytes of the file keep the entire contents in
memory.
</p>
<p>
To fix this problem one can copy the interesting data to a new slice before
returning it:
</p>
{{code "/doc/progs/slices.go" `/CopyDigits/` `/STOP/`}}
<p>
A more concise version of this function could be constructed by using
<code>append</code>. This is left as an exercise for the reader.
</p>
<p>
<b>Further Reading</b>
</p>
<p>
<a href="/doc/effective_go.html">Effective Go</a> contains an
in-depth treatment of <a href="/doc/effective_go.html#slices">slices</a>
and <a href="/doc/effective_go.html#arrays">arrays</a>,
and the Go <a href="/doc/go_spec.html">language specification</a>
defines <a href="/doc/go_spec.html#Slice_types">slices</a> and their
<a href="/doc/go_spec.html#Length_and_capacity">associated</a>
<a href="/doc/go_spec.html#Making_slices_maps_and_channels">helper</a>
<a href="/doc/go_spec.html#Appending_and_copying_slices">functions</a>.
</p>

View File

@@ -1,6 +0,0 @@
<h1>Editing {{.Title |html}}</h1>
<form action="/save/{{.Title |html}}" method="POST">
<div><textarea name="body" rows="20" cols="80">{{printf "%s" .Body |html}}</textarea></div>
<div><input type="submit" value="Save"></div>
</form>

View File

@@ -1,5 +0,0 @@
<h1>{{.Title |html}}</h1>
<p>[<a href="/edit/{{.Title |html}}">edit</a>]</p>
<div>{{printf "%s" .Body |html}}</div>

BIN
doc/button_background.png Normal file

Binary file not shown.

After

Width:  |  Height:  |  Size: 126 B

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@@ -1,103 +0,0 @@
<!--{
"Title": "Command Documentation",
"Path": "/doc/cmd"
}-->
<p>
There is a suite of programs to build and process Go source code.
Instead of being run directly, programs in the suite are usually invoked
by the <a href="/cmd/go/">go</a> program.
</p>
<p>
The most common way to run these programs is as a subcommand of the go program,
for instance as <code>go fmt</code>. Run like this, the command operates on
complete packages of Go source code, with the go program invoking the
underlying binary with arguments appropriate to package-level processing.
</p>
<p>
The programs can also be run as stand-alone binaries, with unmodified arguments,
using the go <code>tool</code> subcommand, such as <code>go tool vet</code>.
This style of invocation allows, for instance, checking a single source file
rather than an entire package: <code>go tool vet myprogram.go</code> as
compared to <code>go vet mypackage</code>.
Some of the commands, such as <code>yacc</code>, are accessible only through
the go <code>tool</code> subcommand.
</p>
<p>
Finally, two of the commands, <code>fmt</code> and <code>doc</code>, are also
installed as regular binaries called <code>gofmt</code> and <code>godoc</code>
because they are so often referenced.
</p>
<p>
Click on the links for more documentation, invocation methods, and usage details.
</p>
<table class="dir">
<tr>
<th>Name</th>
<th>&nbsp;&nbsp;&nbsp;&nbsp;</th>
<th>Synopsis</th>
</tr>
<tr>
<td><a href="/cmd/go/">go</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>
The <code>go</code> program manages Go source code and runs the other
commands listed here.
See the command docs for usage
details.
<br><br>
</td>
</tr>
<tr>
<td><a href="/cmd/cgo/">cgo</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Cgo enables the creation of Go packages that call C code.</td>
</tr>
<tr>
<td><a href="/cmd/fix/">fix</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Fix finds Go programs that use old features of the language and libraries
and rewrites them to use newer ones.</td>
</tr>
<tr>
<td><a href="/cmd/go/">doc</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Doc extracts and generates documentation for Go packages, it is also available as
an independent <a href="/cmd/godoc/">godoc</a> command with more general options.</td>
</tr>
<tr>
<td><a href="/cmd/go/">fmt</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Fmt formats Go packages, it is also available as an independent <a href="/cmd/gofmt/">
gofmt</a> command with more general options.</td>
</tr>
<tr>
<td><a href="/cmd/vet/">vet</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Vet examines Go source code and reports suspicious constructs, such as Printf
calls whose arguments do not align with the format string.</td>
</tr>
<tr>
<td><a href="/cmd/yacc/">yacc</a></td>
<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
<td>Yacc is a version of yacc that generates parsers implemented in Go.</td>
</tr>
</table>
<p>
This is an abridged list. See the <a href="/cmd/">full command reference</a>
for documentation of the compilers and more.
</p>

View File

@@ -1,158 +1,164 @@
<!--{
"Title": "How to Write Go Code"
}-->
<!-- How to Write Go Code -->
<h2 id="Introduction">Introduction</h2>
<p>
This document demonstrates the development of a simple Go package and
introduces the <a href="/cmd/go/">go command</a>, the standard way to fetch,
build, and install Go packages and commands.
</p>
<h2 id="GOPATH">Code organization</h2>
<h3><code>GOPATH</code> and workspaces</h3>
<p>
One of Go's design goals is to make writing software easier. To that end, the
<code>go</code> command doesn't use Makefiles or other configuration files to
guide program construction. Instead, it uses the source code to find
dependencies and determine build conditions. This means your source code and
build scripts are always in sync; they are one and the same.
This document explains how to write a new package
and how to test code.
It assumes you have installed Go using the
<a href="install.html">installation instructions</a>.
</p>
<p>
The one thing you must do is set a <code>GOPATH</code> environment variable.
<code>GOPATH</code> tells the <code>go</code> command (and other related tools)
where to find and install the Go packages on your system.
Before embarking on a change to an existing
package or the creation of a new package,
be sure to send mail to the
<a href="http://groups.google.com/group/golang-nuts">mailing list</a>
to let people know what you are thinking of doing.
Doing so helps avoid duplication of effort and
enables discussions about design before any code
has been written.
</p>
<h2 id="Community_resources">Community resources</h2>
<p>
For real-time help, there may be users or developers on
<code>#go-nuts</code> on the <a href="http://freenode.net/">Freenode</a> IRC server.
</p>
<p>
<code>GOPATH</code> is a list of paths. It shares the syntax of your system's
<code>PATH</code> environment variable. A typical <code>GOPATH</code> on
a Unix system might look like this:
The official mailing list for discussion of the Go language is
<a href="http://groups.google.com/group/golang-nuts">Go Nuts</a>.
</p>
<p>
Bugs can be reported using the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
</p>
<p>
For those who wish to keep up with development,
there is another mailing list, <a href="http://groups.google.com/group/golang-checkins">golang-checkins</a>,
that receives a message summarizing each checkin to the Go repository.
</p>
<h2 id="New_package">Creating a new package</h2>
<p>
The source code for the package with import path
<code>x/y</code> is, by convention, kept in the
directory <code>$GOROOT/src/pkg/x/y</code>.
</p>
<h3>Makefile</h3>
<p>
It would be nice to have Go-specific tools that
inspect the source files to determine what to build and in
what order, but for now, Go uses GNU <code>make</code>.
Thus, the first file to create in a new package directory is
usually the <code>Makefile</code>.
The basic form used in the Go source tree
is illustrated by <a href="../src/pkg/container/vector/Makefile"><code>src/pkg/container/vector/Makefile</code></a>:
</p>
<pre>
GOPATH=/home/user/ext:/home/user/mygo
include ../../../Make.inc
TARG=container/vector
GOFILES=\
intvector.go\
stringvector.go\
vector.go\
include ../../../Make.pkg
</pre>
<p>
(On a Windows system use semicolons as the path separator instead of colons.)
</p>
<p>
Each path in the list (in this case <code>/home/user/ext</code> or
<code>/home/user/mygo</code>) specifies the location of a <i>workspace</i>.
A workspace contains Go source files and their associated package objects, and
command executables. It has a prescribed structure of three subdirectories:
</p>
<ul>
<li><code>src</code> contains Go source files,
<li><code>pkg</code> contains compiled package objects, and
<li><code>bin</code> contains executable commands.
</ul>
<p>
Subdirectories of the <code>src</code> directory hold independent packages, and
all source files (<code>.go</code>, <code>.c</code>, <code>.h</code>, and
<code>.s</code>) in each subdirectory are elements of that subdirectory's
package.
</p>
<p>
When building a program that imports the package "<code>widget</code>" the
<code>go</code> command looks for <code>src/pkg/widget</code> inside the Go root,
and then&mdash;if the package source isn't found there&mdash;it searches
for <code>src/widget</code> inside each workspace in order.
</p>
<p>
Multiple workspaces can offer some flexibility and convenience, but for now
we'll concern ourselves with only a single workspace.
</p>
<p>
Let's work through a simple example. First, create a <code>$HOME/mygo</code>
directory and its <code>src</code> subdirectory:
Outside the Go source tree (for personal packages), the standard form is
</p>
<pre>
$ mkdir -p $HOME/mygo/src # create a place to put source code
include $(GOROOT)/src/Make.inc
TARG=mypackage
GOFILES=\
my1.go\
my2.go\
include $(GOROOT)/src/Make.pkg
</pre>
<p>
Next, set it as the <code>GOPATH</code>. You should also add the
<code>bin</code> subdirectory to your <code>PATH</code> environment variable so
that you can run the commands therein without specifying their full path.
To do this, add the following lines to <code>$HOME/.profile</code> (or
equivalent):
The first and last lines <code>include</code> standard definitions and rules.
Packages maintained in the standard Go tree use a relative path (instead of
<code>$(GOROOT)/src</code>) so that <code>make</code> will work correctly
even if <code>$(GOROOT)</code> contains spaces.
This makes it easy for programmers to try Go.
</p>
<p>
If you have not set <code>$GOROOT</code> in your environment,
you must run <code>gomake</code> to use this form of makefile.
<code>Gomake</code> also takes care to invoke GNU Make
even on systems where it is installed as <code>gmake</code>
rather than <code>make</code>.
</p>
<p>
<code>TARG</code> is the target install path for the package,
the string that clients will use to import it.
Inside the Go tree, this string should be the same as the directory
in which the <code>Makefile</code> appears, with the
<code>$GOROOT/src/pkg/</code> prefix removed.
Outside the Go tree, you can use any <code>TARG</code> you
want that doesn't conflict with the standard Go package names.
A common convention is to use an identifying top-level name
to group your packages: <code>myname/tree</code>, <code>myname/filter</code>, etc.
Note that even if you keep your package source outside the
Go tree, running <code>make install</code> installs your
package binaries in the standard location&mdash;<code>$GOROOT/pkg</code>&mdash;to
make it easy to find them.
</p>
<p>
<code>GOFILES</code> is a list of source files to compile to
create the package. The trailing <code>\</code> characters
allow the list to be split onto multiple lines
for easy sorting.
</p>
<p>
If you create a new package directory in the Go tree, add it to the list in
<code>$GOROOT/src/pkg/Makefile</code> so that it
is included in the standard build. Then run:
<pre>
export GOPATH=$HOME/mygo
export PATH=$PATH:$HOME/mygo/bin
cd $GOROOT/src/pkg
./deps.bash
</pre>
<h3>Import paths</h3>
<p>
The standard packages are given short import paths such as <code>"fmt"</code>
and <code>"net/http"</code> for convenience.
For your own projects, it is important to choose a base import path that is
unlikely to collide with future additions to the standard library or other
external libraries.
to update the dependency file <code>Make.deps</code>.
(This happens automatically each time you run <code>all.bash</code>
or <code>make.bash</code>.)
</p>
<p>
The best way to choose an import path is to use the location of your version
control repository.
For instance, if your source repository is at <code>example.com</code>
or <code>code.google.com/p/example</code>, you should begin your package
paths with that URL, as in "<code>example.com/foo/bar</code>" or
"<code>code.google.com/p/example/foo/bar</code>".
Using this convention, the <code>go</code> command can automatically check out and
build the source code by its import path alone.
If you change the imports of an existing package,
you do not need to edit <code>$GOROOT/src/pkg/Makefile</code>
but you will still need to run <code>deps.bash</code> as above.
</p>
<p>
If you don't intend to install your code in this way, you should at
least use a unique prefix like "<code>widgets/</code>", as in
"<code>widgets/foo/bar</code>". A good rule is to use a prefix such as your
company or project name, since it is unlikely to be used by another group.
</p>
<h3>Go source files</h3>
<p>
We'll use <code>example/</code> as our base import path:
</p>
<pre>
$ mkdir -p $GOPATH/src/example
</pre>
<h3>Package names</h3>
<p>
The first statement in a Go source file should be
</p>
<pre>
package <i>name</i>
</pre>
<p>
where <code><i>name</i></code> is the package's default name for imports.
The first statement in each of the source files listed in the <code>Makefile</code>
should be <code>package <i>name</i></code>, where <code><i>name</i></code>
is the package's default name for imports.
(All files in a package must use the same <code><i>name</i></code>.)
</p>
<p>
Go's convention is that the package name is the last element of the
import path: the package imported as "<code>crypto/rot13</code>"
import path: the package imported as <code>"crypto/rot13"</code>
should be named <code>rot13</code>.
There is no requirement that package names be unique
across all packages linked into a single binary,
@@ -160,344 +166,203 @@ only that the import paths (their full file names) be unique.
</p>
<p>
Create a new package under <code>example</code> called <code>newmath</code>:
Go compiles all the source files in a package at once, so one file
can refer to constants, variables, types, and functions in another
file without special arrangement or declarations.
</p>
<p>
Writing clean, idiomatic Go code is beyond the scope of this document.
<a href="effective_go.html">Effective Go</a> is an introduction to
that topic.
</p>
<h2 id="Building_programs">Building programs</h2>
<p>To build a Go program with gomake, create a Makefile alongside your program's
source files. It should be similar to the example above, but include
<code>Make.cmd</code> instead of <code>Make.pkg</code>:
<pre>
$ cd $GOPATH/src/example
$ mkdir newmath
include $(GOROOT)/src/Make.inc
TARG=helloworld
GOFILES=\
helloworld.go\
include $(GOROOT)/src/Make.cmd
</pre>
<p>
Then create a file named <code>$GOPATH/src/example/newmath/sqrt.go</code>
containing the following Go code:
</p>
<pre>
// Package newmath is a trivial example package.
package newmath
// Sqrt returns an approximation to the square root of x.
func Sqrt(x float64) float64 {
// This is a terrible implementation.
// Real code should import "math" and use math.Sqrt.
z := 0.0
for i := 0; i < 1000; i++ {
z -= (z*z - x) / (2 * x)
}
return z
}
</pre>
<p>
This package is imported by the path name of the directory it's in, starting
after the <code>src</code> component:
</p>
<pre>
import "example/newmath"
</pre>
<p>
See <a href="/doc/effective_go.html#names">Effective Go</a> to learn more about
Go's naming conventions.
</p>
<h2>Building and installing</h2>
<p>
The <code>go</code> command comprises several subcommands, the most central being
<code>install</code>. Running <code>go install <i>importpath</i></code> builds
and installs a package and its dependencies.
<p>Running <code>gomake</code> will compile <code>helloworld.go</code>
and produce an executable named <code>helloworld</code> in the current
directory.
</p>
<p>
To "install a package" means to write the package object or executable command
to the <code>pkg</code> or <code>bin</code> subdirectory of the workspace in
which the source resides.
Running <code>gomake install</code> will build <code>helloworld</code> if
necessary and copy it to the <code>$GOBIN</code> directory
(<code>$GOROOT/bin/</code> is the default).
</p>
<h3>Building a package</h3>
<p>
To build and install the <code>newmath</code> package, type
</p>
<pre>
$ go install example/newmath
</pre>
<p>
This command will produce no output if the package and its dependencies
are built and installed correctly.
</p>
<p>
As a convenience, the <code>go</code> command will assume the current directory
if no import path is specified on the command line. This sequence of commands
has the same affect as the one above:
</p>
<pre>
$ cd $GOPATH/src/example/newmath
$ go install
</pre>
<p>
The resulting workspace directory tree (assuming we're running Linux on a 64-bit
system) looks like this:
</p>
<pre>
pkg/
linux_amd64/
example/
newmath.a # package object
src/
example/
newmath/
sqrt.go # package source
</pre>
<h3>Building a command</h3>
<p>
The <code>go</code> command treats code belonging to <code>package main</code> as
an executable command and installs the package binary to the
<code>GOPATH</code>'s <code>bin</code> subdirectory.
</p>
<p>
Add a command named <code>hello</code> to the source tree.
First create the <code>example/hello</code> directory:
</p>
<pre>
$ cd $GOPATH/src/example
$ mkdir hello
</pre>
<p>
Then create the file <code>$GOPATH/src/example/hello/hello.go</code>
containing the following Go code.
</p>
<pre>
// Hello is a trivial example of a main package.
package main
import (
"example/newmath"
"fmt"
)
func main() {
fmt.Printf("Hello, world. Sqrt(2) = %v\n", newmath.Sqrt(2))
}
</pre>
<p>
Next, run <code>go install</code>, which builds and installs the binary to
<code>$GOPATH/bin</code>:
</p>
<pre>
$ go install example/hello
</pre>
<p>
To run the program, invoke it by name as you would any other command:
</p>
<pre>
$ $GOPATH/bin/hello
Hello, world. Sqrt(2) = 1.414213562373095
</pre>
<p>
If you added <code>$HOME/mygo/bin</code> to your <code>PATH</code>, you may omit
the path to the executable:
</p>
<pre>
$ hello
Hello, world. Sqrt(2) = 1.414213562373095
</pre>
<p>
The workspace directory tree now looks like this:
</p>
<pre>
bin/
hello # command executable
pkg/
linux_amd64/
example/
newmath.a # package object
src/
example/
hello/
hello.go # command source
newmath/
sqrt.go # package source
</pre>
<p>
The <code>go</code> command also provides a <code>build</code> command, which is
like <code>install</code> except it builds all objects in a temporary directory
and does not install them under <code>pkg</code> or <code>bin</code>.
When building a command an executable named after the last element of the
import path is written to the current directory. When building a package,
<code>go build</code> serves merely to test that the package and its
dependencies can be built. (The resulting package object is thrown away.)
</p>
<h2 id="Testing">Testing</h2>
<p>
Go has a lightweight test framework composed of the <code>go test</code>
command and the <code>testing</code> package.
</p>
<p>
Go has a lightweight test framework known as <code>gotest</code>.
You write a test by creating a file with a name ending in <code>_test.go</code>
that contains functions named <code>TestXXX</code> with signature
<code>func (t *testing.T)</code>.
that contains functions named <code>TestXXX</code> with signature <code>func (t *testing.T)</code>.
The test framework runs each such function;
if the function calls a failure function such as <code>t.Error</code> or
<code>t.Fail</code>, the test is considered to have failed.
if the function calls a failure function such as <code>t.Error</code> or <code>t.Fail</code>, the test is considered to have failed.
The <a href="/cmd/gotest/">gotest command documentation</a>
and the <a href="/pkg/testing/">testing package documentation</a> give more detail.
</p>
<p>
Add a test to the <code>newmath</code> package by creating the file
<code>$GOPATH/src/example/newmath/sqrt_test.go</code> containing the following
Go code.
The <code>*_test.go</code> files should not be listed in the <code>Makefile</code>.
</p>
<p>
To run the test, run either <code>make test</code> or <code>gotest</code>
(they are equivalent).
To run only the tests in a single test file, for instance <code>one_test.go</code>,
run <code>gotest one_test.go</code>.
</p>
<p>
If your change affects performance, add a <code>Benchmark</code> function
(see the <a href="/cmd/gotest/">gotest command documentation</a>)
and run it using <code>gotest -test.bench=.</code>.
</p>
<p>
Once your new code is tested and working,
it's time to get it <a href="contribute.html">reviewed and submitted</a>.
</p>
<h2 id="pkg_example">An example package with tests</h2>
<p>
This example package, <code>numbers</code>, consists of the function
<code>Double</code>, which takes an <code>int</code> and returns that value
multiplied by 2. It consists of three files.
</p>
<p>
First, the package implementation, <code>numbers.go</code>:
</p>
<pre>
package newmath
package numbers
import "testing"
func TestSqrt(t *testing.T) {
const in, out = 9, 3
if x := Sqrt(in); x != out {
t.Errorf("Sqrt(%v) = %v, want %v", in, x, out)
}
func Double(i int) int {
return i * 2
}
</pre>
<p>
Now run the test with <code>go test</code>:
Next, the tests, <code>numbers_test.go</code>:
</p>
<pre>
$ go test example/newmath
ok example/newmath
package numbers
import (
"testing"
)
type doubleTest struct {
in, out int
}
var doubleTests = []doubleTest{
doubleTest{1, 2},
doubleTest{2, 4},
doubleTest{-5, -10},
}
func TestDouble(t *testing.T) {
for _, dt := range doubleTests {
v := Double(dt.in)
if v != dt.out {
t.Errorf("Double(%d) = %d, want %d.", dt.in, v, dt.out)
}
}
}
</pre>
<p>
Run <code><a href="/cmd/go/#Test_packages">go help test</a></code> and see the
<a href="/pkg/testing/">testing package documentation</a> for more detail.
</p>
<h2 id="remote">Remote packages</h2>
<p>
An import path can describe how to obtain the package source code using a
revision control system such as Git or Mercurial. The <code>go</code> command uses
this property to automatically fetch packages from remote repositories.
For instance, the examples described in this document are also kept in a
Mercurial repository hosted at Google Code,
<code><a href="http://code.google.com/p/go.example">code.google.com/p/go.example</a></code>.
If you include the repository URL in the package's import path,
<code>go get</code> will fetch, build, and install it automatically:
Finally, the <code>Makefile</code>:
</p>
<pre>
$ go get code.google.com/p/go.example/hello
$ $GOPATH/bin/hello
Hello, world. Sqrt(2) = 1.414213562373095
include $(GOROOT)/src/Make.inc
TARG=numbers
GOFILES=\
numbers.go\
include $(GOROOT)/src/Make.pkg
</pre>
<p>
If the specified package is not present in a workspace, <code>go get</code>
will place it inside the first workspace specified by <code>GOPATH</code>.
(If the package does already exist, <code>go get</code> skips the remote
fetch and behaves the same as <code>go install</code>.)
Running <code>gomake install</code> will build and install the package to
the <code>$GOROOT/pkg/</code> directory (it can then be used by any
program on the system).
</p>
<p>
After issuing the above <code>go get</code> command, the workspace directory
tree should now now look like this:
Running <code>gomake test</code> (or just running the command
<code>gotest</code>) will rebuild the package, including the
<code>numbers_test.go</code> file, and then run the <code>TestDouble</code>
function. The output "<code>PASS</code>" indicates that all tests passed
successfully. Breaking the implementation by changing the multiplier from
<code>2</code> to <code>3</code> will allow you to see how failing tests are
reported.
</p>
<p>
See the <a href="/cmd/gotest/">gotest documentation</a> and the
<a href="/pkg/testing/">testing package</a> for more detail.
</p>
<h2 id="arch_os_specific">Architecture- and operating system-specific code</h2>
<p>First, a disclaimer: very few Go packages should need to know about the
hardware and operating system they run on. In the vast majority of cases the
language and standard library handle most portability issues. This section is
a guide for experienced systems programmers who have a good reason to write
platform-specific code, such as assembly-language support for fast
trigonometric functions or code that implements a common interface above
different operating systems.</p>
<p>To compile such code, use the <code>$GOOS</code> and <code>$GOARCH</code>
<a href="/doc/install.html#environment">environment variables</a> in your
source file names and <code>Makefile</code>.</p>
<p>For example, this <code>Makefile</code> describes a package that builds on
different operating systems by parameterizing the file name with
<code>$GOOS</code>.</p>
<pre>
include $(GOROOT)/src/Make.inc
TARG=mypackage
GOFILES=\
my.go\
my_$(GOOS).go\
include $(GOROOT)/src/Make.pkg
</pre>
<p>The OS-specific code goes in <code>my_linux.go</code>,
<code>my_darwin.go</code>, and so on.</p>
<p>If you follow these conventional parameterizations, tools such as
<a href="/cmd/goinstall/">goinstall</a> will work seamlessly with your package:
</p>
<pre>
bin/
hello # command executable
pkg/
linux_amd64/
code.google.com/p/go.example/
newmath.a # package object
example/
newmath.a # package object
src/
code.google.com/p/go.example/
hello/
hello.go # command source
newmath/
sqrt.go # package source
sqrt_test.go # test source
example/
hello/
hello.go # command source
newmath/
sqrt.go # package source
sqrt_test.go # test source
my_$(GOOS).go
my_$(GOARCH).go
my_$(GOOS)_$(GOARCH).go
</pre>
<p>
The <code>hello</code> command hosted at Google Code depends on the
<code>newmath</code> package within the same repository. The imports in
<code>hello.go</code> file use the same import path convention, so the <code>go
get</code> command is able to locate and install the dependent package, too.
</p>
<pre>
import "code.google.com/p/go.example/newmath"
</pre>
<p>
This convention is the easiest way to make your Go packages available for
others to use.
The <a href="http://godashboard.appspot.com/package">Go Package Dashboard</a>
displays a list of packages recently installed with the <code>go</code> command.
</p>
<p>
For more information on using remote repositories with the <code>go</code> command, see
<code><a href="/cmd/go/#Remote_import_path_syntax">go help remote</a></code>.
</p>
<h2 id="more">Further reading</h2>
<p>
See <a href="/doc/effective_go.html">Effective Go</a> for tips on writing
clear, idiomatic Go code.
</p>
<p>
Take <a href="http://tour.golang.org/">A Tour of Go</a> to learn the language
proper.
</p>
<p>
Visit the <a href="/doc/#articles">documentation page</a> for a set of in-depth
articles about the Go language and its libraries and tools.
</p>
<p>The same holds for <code>.s</code> (assembly) files.</p>

View File

@@ -2,19 +2,24 @@
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file.
include ../../../src/Make.inc
all: index.html
CLEANFILES:=srcextract.bin htmlify.bin get.bin
include ../../../src/Make.common
index.html: wiki.html srcextract.bin htmlify.bin
CLEANFILES+=index.html srcextract.bin htmlify.bin get.bin
index.html: srcextract.bin htmlify.bin
PATH=.:$$PATH awk '/^!/{system(substr($$0,2)); next} {print}' < wiki.html | tr -d '\r' > index.html
test: get.bin
bash ./test.sh
rm -f get.6 get.bin
%.bin: %.go
go build -o $@ $^
%.bin: %.$O
$(LD) -o $@ $<
%.$O: %.go
$(GC) $*.go
clean:
rm -f $(CLEANFILES)

View File

@@ -0,0 +1,6 @@
<h1>Editing {Title}</h1>
<form action="/save/{Title}" method="POST">
<div><textarea name="body" rows="20" cols="80">{Body|html}</textarea></div>
<div><input type="submit" value="Save"></div>
</form>

View File

@@ -1,15 +1,11 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"errors"
"html/template"
"http"
"io/ioutil"
"net/http"
"os"
"regexp"
"template"
)
type Page struct {
@@ -17,12 +13,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {
@@ -65,21 +61,21 @@ func saveHandler(w http.ResponseWriter, r *http.Request) {
p := &Page{Title: title, Body: []byte(body)}
err = p.save()
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
return
}
http.Redirect(w, r, "/view/"+title, http.StatusFound)
}
func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
t, err := template.ParseFiles(tmpl + ".html")
t, err := template.ParseFile(tmpl+".html", nil)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
return
}
err = t.Execute(w, p)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
}
}
@@ -87,11 +83,11 @@ const lenPath = len("/view/")
var titleValidator = regexp.MustCompile("^[a-zA-Z0-9]+$")
func getTitle(w http.ResponseWriter, r *http.Request) (title string, err error) {
func getTitle(w http.ResponseWriter, r *http.Request) (title string, err os.Error) {
title = r.URL.Path[lenPath:]
if !titleValidator.MatchString(title) {
http.NotFound(w, r)
err = errors.New("Invalid Page Title")
err = os.NewError("Invalid Page Title")
}
return
}

View File

@@ -1,13 +1,10 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"html/template"
"http"
"io/ioutil"
"net/http"
"os"
"template"
)
type Page struct {
@@ -15,12 +12,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {
@@ -37,14 +34,14 @@ func editHandler(w http.ResponseWriter, r *http.Request) {
if err != nil {
p = &Page{Title: title}
}
t, _ := template.ParseFiles("edit.html")
t, _ := template.ParseFile("edit.html", nil)
t.Execute(w, p)
}
func viewHandler(w http.ResponseWriter, r *http.Request) {
title := r.URL.Path[lenPath:]
p, _ := loadPage(title)
t, _ := template.ParseFiles("view.html")
t, _ := template.ParseFile("view.html", nil)
t.Execute(w, p)
}

View File

@@ -1,14 +1,11 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"html/template"
"http"
"io/ioutil"
"net/http"
"os"
"regexp"
"template"
)
type Page struct {
@@ -16,12 +13,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {
@@ -52,21 +49,21 @@ func saveHandler(w http.ResponseWriter, r *http.Request, title string) {
p := &Page{Title: title, Body: []byte(body)}
err := p.save()
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
return
}
http.Redirect(w, r, "/view/"+title, http.StatusFound)
}
func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
t, err := template.ParseFiles(tmpl + ".html")
t, err := template.ParseFile(tmpl+".html", nil)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
return
}
err = t.Execute(w, p)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
}
}

View File

@@ -1,13 +1,10 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"html/template"
"http"
"io/ioutil"
"net/http"
"os"
"template"
)
type Page struct {
@@ -15,12 +12,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {
@@ -55,7 +52,7 @@ func saveHandler(w http.ResponseWriter, r *http.Request) {
}
func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
t, _ := template.ParseFiles(tmpl + ".html")
t, _ := template.ParseFile(tmpl+".html", nil)
t.Execute(w, p)
}

View File

@@ -1,14 +1,11 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"html/template"
"http"
"io/ioutil"
"net/http"
"os"
"regexp"
"template"
)
type Page struct {
@@ -16,12 +13,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {
@@ -52,18 +49,24 @@ func saveHandler(w http.ResponseWriter, r *http.Request, title string) {
p := &Page{Title: title, Body: []byte(body)}
err := p.save()
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
return
}
http.Redirect(w, r, "/view/"+title, http.StatusFound)
}
var templates = template.Must(template.ParseFiles("edit.html", "view.html"))
var templates = make(map[string]*template.Template)
func init() {
for _, tmpl := range []string{"edit", "view"} {
templates[tmpl] = template.MustParseFile(tmpl+".html", nil)
}
}
func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
err := templates.ExecuteTemplate(w, tmpl+".html", p)
err := templates[tmpl].Execute(w, p)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
http.Error(w, err.String(), http.StatusInternalServerError)
}
}

View File

@@ -1,16 +1,12 @@
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"http"
"flag"
"fmt"
"io"
"log"
"net"
"net/http"
"os"
"strings"
)
@@ -36,12 +32,12 @@ func main() {
log.Fatal("no url supplied")
}
var r *http.Response
var err error
var err os.Error
if *post != "" {
b := strings.NewReader(*post)
r, err = http.Post(url, "application/x-www-form-urlencoded", b)
} else {
r, err = http.Get(url)
r, _, err = http.Get(url)
}
if err != nil {
log.Fatal(err)

View File

@@ -0,0 +1,12 @@
package main
import (
"os"
"template"
"io/ioutil"
)
func main() {
b, _ := ioutil.ReadAll(os.Stdin)
template.HTMLFormatter(os.Stdout, "", b)
}

View File

@@ -2,7 +2,7 @@ package main
import (
"fmt"
"net/http"
"http"
)
func handler(w http.ResponseWriter, r *http.Request) {

1003
doc/codelab/wiki/index.html Normal file

File diff suppressed because it is too large Load Diff

View File

@@ -1,13 +1,10 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"http"
"io/ioutil"
"net/http"
"os"
)
type Page struct {
@@ -15,12 +12,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {

View File

@@ -1,12 +1,9 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"io/ioutil"
"os"
)
type Page struct {
@@ -14,7 +11,7 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}

View File

@@ -1,12 +1,9 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"io/ioutil"
"os"
)
type Page struct {
@@ -14,12 +11,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {

View File

@@ -1,13 +1,10 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"http"
"io/ioutil"
"net/http"
"os"
)
type Page struct {
@@ -15,12 +12,12 @@ type Page struct {
Body []byte
}
func (p *Page) save() error {
func (p *Page) save() os.Error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
func loadPage(title string) (*Page, error) {
func loadPage(title string) (*Page, os.Error) {
filename := title + ".txt"
body, err := ioutil.ReadFile(filename)
if err != nil {

View File

@@ -1,19 +1,15 @@
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"bytes"
"flag"
"go/ast"
"go/parser"
"go/printer"
"go/ast"
"go/token"
"log"
"os"
"text/template"
"template"
)
var (

View File

@@ -1,7 +1,4 @@
#!/usr/bin/env bash
# Copyright 2010 The Go Authors. All rights reserved.
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file.
set -e
wiki_pid=
@@ -11,10 +8,10 @@ cleanup() {
}
trap cleanup 0 INT
go build -o get.bin get.go
gomake get.bin
addr=$(./get.bin -addr)
sed s/:8080/$addr/ < final.go > final-test.go
go build -o final-test.bin final-test.go
gomake final-test.bin
(./final-test.bin) &
wiki_pid=$!

View File

@@ -0,0 +1,5 @@
<h1>{Title}</h1>
<p>[<a href="/edit/{Title}">edit</a>]</p>
<div>{Body}</div>

View File

@@ -1,17 +1,13 @@
<!--{
"Title": "Writing Web Applications",
"Template": true
}-->
<!-- Codelab: Writing Web Applications -->
<h2>Introduction</h2>
<p>
Covered in this tutorial:
Covered in this codelab:
</p>
<ul>
<li>Creating a data structure with load and save methods</li>
<li>Using the <code>net/http</code> package to build web applications
<li>Using the <code>html/template</code> package to process HTML templates</li>
<li>Using the <code>http</code> package to build web applications
<li>Using the <code>template</code> package to process HTML templates</li>
<li>Using the <code>regexp</code> package to validate user input</li>
<li>Using closures</li>
</ul>
@@ -22,27 +18,30 @@ Assumed knowledge:
<ul>
<li>Programming experience</li>
<li>Understanding of basic web technologies (HTTP, HTML)</li>
<li>Some UNIX/DOS command-line knowledge</li>
<li>Some UNIX command-line knowledge</li>
</ul>
<h2>Getting Started</h2>
<p>
At present, you need to have a FreeBSD, Linux, OS X, or Windows machine to run Go.
We will use <code>$</code> to represent the command prompt.
At present, you need to have a Linux, OS X, or FreeBSD machine to run Go. If
you don't have access to one, you could set up a Linux Virtual Machine (using
<a href="http://www.virtualbox.org/">VirtualBox</a> or similar) or a
<a href="http://www.google.com/search?q=virtual+private+server">Virtual
Private Server</a>.
</p>
<p>
Install Go (see the <a href="/doc/install">Installation Instructions</a>).
Install Go (see the <a href="http://golang.org/doc/install.html">Installation Instructions</a>).
</p>
<p>
Make a new directory for this tutorial inside your <code>GOPATH</code> and cd to it:
Make a new directory for this codelab and cd to it:
</p>
<pre>
$ mkdir gowiki
$ cd gowiki
$ mkdir ~/gowiki
$ cd ~/gowiki
</pre>
<p>
@@ -56,13 +55,15 @@ package main
import (
"fmt"
"io/ioutil"
"os"
)
</pre>
<p>
We import the <code>fmt</code> and <code>ioutil</code> packages from the Go
standard library. Later, as we implement additional functionality, we will
add more packages to this <code>import</code> declaration.
We import the <code>fmt</code>, <code>ioutil</code> and <code>os</code>
packages from the Go standard library. Later, as we implement additional
functionality, we will add more packages to this <code>import</code>
declaration.
</p>
<h2>Data Structures</h2>
@@ -74,12 +75,14 @@ Here, we define <code>Page</code> as a struct with two fields representing
the title and body.
</p>
{{code "doc/articles/wiki/part1.go" `/^type Page/` `/}/`}}
<pre>
!srcextract.bin -src=part1.go -name=Page
</pre>
<p>
The type <code>[]byte</code> means "a <code>byte</code> slice".
(See <a href="/doc/articles/slices_usage_and_internals.html">Slices: usage and
internals</a> for more on slices.)
(See <a href="http://golang.org/doc/effective_go.html#slices">Effective Go</a>
for more on slices.)
The <code>Body</code> element is a <code>[]byte</code> rather than
<code>string</code> because that is the type expected by the <code>io</code>
libraries we will use, as you'll see below.
@@ -91,12 +94,14 @@ But what about persistent storage? We can address that by creating a
<code>save</code> method on <code>Page</code>:
</p>
{{code "doc/articles/wiki/part1.go" `/^func.*Page.*save/` `/}/`}}
<pre>
!srcextract.bin -src=part1.go -name=save
</pre>
<p>
This method's signature reads: "This is a method named <code>save</code> that
takes as its receiver <code>p</code>, a pointer to <code>Page</code> . It takes
no parameters, and returns a value of type <code>error</code>."
no parameters, and returns a value of type <code>os.Error</code>."
</p>
<p>
@@ -105,7 +110,7 @@ file. For simplicity, we will use the <code>Title</code> as the file name.
</p>
<p>
The <code>save</code> method returns an <code>error</code> value because
The <code>save</code> method returns an <code>os.Error</code> value because
that is the return type of <code>WriteFile</code> (a standard library function
that writes a byte slice to a file). The <code>save</code> method returns the
error value, to let the application handle it should anything go wrong while
@@ -125,7 +130,9 @@ read-write permissions for the current user only. (See the Unix man page
We will want to load pages, too:
</p>
{{code "doc/articles/wiki/part1-noerror.go" `/^func loadPage/` `/^}/`}}
<pre>
!srcextract.bin -src=part1-noerror.go -name=loadPage
</pre>
<p>
The function <code>loadPage</code> constructs the file name from
@@ -135,7 +142,7 @@ The function <code>loadPage</code> constructs the file name from
<p>
Functions can return multiple values. The standard library function
<code>io.ReadFile</code> returns <code>[]byte</code> and <code>error</code>.
<code>io.ReadFile</code> returns <code>[]byte</code> and <code>os.Error</code>.
In <code>loadPage</code>, error isn't being handled yet; the "blank identifier"
represented by the underscore (<code>_</code>) symbol is used to throw away the
error return value (in essence, assigning the value to nothing).
@@ -144,16 +151,19 @@ error return value (in essence, assigning the value to nothing).
<p>
But what happens if <code>ReadFile</code> encounters an error? For example,
the file might not exist. We should not ignore such errors. Let's modify the
function to return <code>*Page</code> and <code>error</code>.
function to return <code>*Page</code> and <code>os.Error</code>.
</p>
{{code "doc/articles/wiki/part1.go" `/^func loadPage/` `/^}/`}}
<pre>
!srcextract.bin -src=part1.go -name=loadPage
</pre>
<p>
Callers of this function can now check the second parameter; if it is
<code>nil</code> then it has successfully loaded a Page. If not, it will be an
<code>error</code> that can be handled by the caller (see the
<a href="/ref/spec#Errors">language specification</a> for details).
<code>os.Error</code> that can be handled by the caller (see the <a
href="http://golang.org/pkg/os/#Error">os package documentation</a> for
details).
</p>
<p>
@@ -162,7 +172,9 @@ load from a file. Let's write a <code>main</code> function to test what we've
written:
</p>
{{code "doc/articles/wiki/part1.go" `/^func main/` `/^}/`}}
<pre>
!srcextract.bin -src=part1.go -name=main
</pre>
<p>
After compiling and executing this code, a file named <code>TestPage.txt</code>
@@ -176,27 +188,31 @@ You can compile and run the program like this:
</p>
<pre>
$ go build wiki.go
$ ./wiki
$ 8g wiki.go
$ 8l wiki.8
$ ./8.out
This is a sample page.
</pre>
<p>
(If you're using Windows you must type "<code>wiki</code>" without the
"<code>./</code>" to run the program.)
(The <code>8g</code> and <code>8l</code> commands are applicable to
<code>GOARCH=386</code>. If you're on an <code>amd64</code> system,
substitute 6's for the 8's.)
</p>
<p>
<a href="part1.go">Click here to view the code we've written so far.</a>
</p>
<h2>Introducing the <code>net/http</code> package (an interlude)</h2>
<h2>Introducing the <code>http</code> package (an interlude)</h2>
<p>
Here's a full working example of a simple web server:
</p>
{{code "doc/articles/wiki/http-sample.go"}}
<pre>
!htmlify.bin < http-sample.go
</pre>
<p>
The <code>main</code> function begins with a call to
@@ -240,17 +256,18 @@ the program would present a page containing:
</p>
<pre>Hi there, I love monkeys!</pre>
<h2>Using <code>net/http</code> to serve wiki pages</h2>
<h2>Using <code>http</code> to serve wiki pages</h2>
<p>
To use the <code>net/http</code> package, it must be imported:
To use the <code>http</code> package, it must be imported:
</p>
<pre>
import (
"fmt"
<b>"net/http"</b>
<b>"http"</b>
"io/ioutil"
"os"
)
</pre>
@@ -258,9 +275,11 @@ import (
Let's create a handler to view a wiki page:
</p>
{{code "doc/articles/wiki/part2.go" `/^const lenPath/`}}
<pre>
!srcextract.bin -src=part2.go -name=lenPath
{{code "doc/articles/wiki/part2.go" `/^func viewHandler/` `/^}/`}}
!srcextract.bin -src=part2.go -name=viewHandler
</pre>
<p>
First, this function extracts the page title from <code>r.URL.Path</code>,
@@ -278,7 +297,7 @@ HTML, and writes it to <code>w</code>, the <code>http.ResponseWriter</code>.
</p>
<p>
Again, note the use of <code>_</code> to ignore the <code>error</code>
Again, note the use of <code>_</code> to ignore the <code>os.Error</code>
return value from <code>loadPage</code>. This is done here for simplicity
and generally considered bad practice. We will attend to this later.
</p>
@@ -289,7 +308,9 @@ initializes <code>http</code> using the <code>viewHandler</code> to handle
any requests under the path <code>/view/</code>.
</p>
{{code "doc/articles/wiki/part2.go" `/^func main/` `/^}/`}}
<pre>
!srcextract.bin -src=part2.go -name=main
</pre>
<p>
<a href="part2.go">Click here to view the code we've written so far.</a>
@@ -297,17 +318,14 @@ any requests under the path <code>/view/</code>.
<p>
Let's create some page data (as <code>test.txt</code>), compile our code, and
try serving a wiki page.
</p>
<p>
Open <code>test.txt</code> file in your editor, and save the string "Hello world" (without quotes)
in it.
try serving a wiki page:
</p>
<pre>
$ go build wiki.go
$ ./wiki
$ echo "Hello world" &gt; test.txt
$ 8g wiki.go
$ 8l wiki.8
$ ./8.out
</pre>
<p>
@@ -329,7 +347,9 @@ form.
First, we add them to <code>main()</code>:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/^func main/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=main
</pre>
<p>
The function <code>editHandler</code> loads the page
@@ -337,24 +357,26 @@ The function <code>editHandler</code> loads the page
and displays an HTML form.
</p>
{{code "doc/articles/wiki/notemplate.go" `/^func editHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=notemplate.go -name=editHandler
</pre>
<p>
This function will work fine, but all that hard-coded HTML is ugly.
Of course, there is a better way.
</p>
<h2>The <code>html/template</code> package</h2>
<h2>The <code>template</code> package</h2>
<p>
The <code>html/template</code> package is part of the Go standard library.
We can use <code>html/template</code> to keep the HTML in a separate file,
allowing us to change the layout of our edit page without modifying the
underlying Go code.
The <code>template</code> package is part of the Go standard library. We can
use <code>template</code> to keep the HTML in a separate file, allowing
us to change the layout of our edit page without modifying the underlying Go
code.
</p>
<p>
First, we must add <code>html/template</code> to the list of imports:
First, we must add <code>template</code> to the list of imports:
</p>
<pre>
@@ -362,7 +384,7 @@ import (
"http"
"io/ioutil"
"os"
<b>"html/template"</b>
<b>"template"</b>
)
</pre>
@@ -371,40 +393,42 @@ Let's create a template file containing the HTML form.
Open a new file named <code>edit.html</code>, and add the following lines:
</p>
{{code "doc/articles/wiki/edit.html"}}
<pre>
!htmlify.bin < edit.html
</pre>
<p>
Modify <code>editHandler</code> to use the template, instead of the hard-coded
HTML:
</p>
{{code "doc/articles/wiki/final-noerror.go" `/^func editHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noerror.go -name=editHandler
</pre>
<p>
The function <code>template.ParseFiles</code> will read the contents of
The function <code>template.ParseFile</code> will read the contents of
<code>edit.html</code> and return a <code>*template.Template</code>.
</p>
<p>
The method <code>t.Execute</code> executes the template, writing the
generated HTML to the <code>http.ResponseWriter</code>.
The <code>.Title</code> and <code>.Body</code> dotted identifiers refer to
<code>p.Title</code> and <code>p.Body</code>.
The method <code>t.Execute</code> replaces all occurrences of
<code>{Title}</code> and <code>{Body}</code> with the values of
<code>p.Title</code> and <code>p.Body</code>, and writes the resultant
HTML to the <code>http.ResponseWriter</code>.
</p>
<p>
Template directives are enclosed in double curly braces.
The <code>printf "%s" .Body</code> instruction is a function call
that outputs <code>.Body</code> as a string instead of a stream of bytes,
the same as a call to <code>fmt.Printf</code>.
The <code>|html</code> part of each directive pipes the value through the
<code>html</code> formatter before outputting it, which escapes HTML
characters (such as replacing <code>&gt;</code> with <code>&amp;gt;</code>),
preventing user data from corrupting the form HTML.
Note that we've used <code>{Body|html}</code> in the above template.
The <code>|html</code> part asks the template engine to pass the value
<code>Body</code> through the <code>html</code> formatter before outputting it,
which escapes HTML characters (such as replacing <code>&gt;</code> with
<code>&amp;gt;</code>).
This will prevent user data from corrupting the form HTML.
</p>
<p>
Now that we've removed the <code>fmt.Fprintf</code> statement, we can remove
Now that we've removed the <code>fmt.Sprintf</code> statement, we can remove
<code>"fmt"</code> from the <code>import</code> list.
</p>
@@ -413,13 +437,17 @@ While we're working with templates, let's create a template for our
<code>viewHandler</code> called <code>view.html</code>:
</p>
{{code "doc/articles/wiki/view.html"}}
<pre>
!htmlify.bin < view.html
</pre>
<p>
Modify <code>viewHandler</code> accordingly:
</p>
{{code "doc/articles/wiki/final-noerror.go" `/^func viewHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noerror.go -name=viewHandler
</pre>
<p>
Notice that we've used almost exactly the same templating code in both
@@ -427,9 +455,13 @@ handlers. Let's remove this duplication by moving the templating code
to its own function:
</p>
{{code "doc/articles/wiki/final-template.go" `/^func viewHandler/` `/^}/`}}
{{code "doc/articles/wiki/final-template.go" `/^func editHandler/` `/^}/`}}
{{code "doc/articles/wiki/final-template.go" `/^func renderTemplate/` `/^}/`}}
<pre>
!srcextract.bin -src=final-template.go -name=viewHandler
!srcextract.bin -src=final-template.go -name=editHandler
!srcextract.bin -src=final-template.go -name=renderTemplate
</pre>
<p>
The handlers are now shorter and simpler.
@@ -438,14 +470,15 @@ The handlers are now shorter and simpler.
<h2>Handling non-existent pages</h2>
<p>
What if you visit <a href="http://localhost:8080/view/APageThatDoesntExist">
<code>/view/APageThatDoesntExist</code></a>? The program will crash. This is
because it ignores the error return value from <code>loadPage</code>. Instead,
if the requested Page doesn't exist, it should redirect the client to the edit
Page so the content may be created:
What if you visit <code>/view/APageThatDoesntExist</code>? The program will
crash. This is because it ignores the error return value from
<code>loadPage</code>. Instead, if the requested Page doesn't exist, it should
redirect the client to the edit Page so the content may be created:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/^func viewHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=viewHandler
</pre>
<p>
The <code>http.Redirect</code> function adds an HTTP status code of
@@ -459,7 +492,9 @@ header to the HTTP response.
The function <code>saveHandler</code> will handle the form submission.
</p>
{{code "doc/articles/wiki/final-template.go" `/^func saveHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-template.go -name=saveHandler
</pre>
<p>
The page title (provided in the URL) and the form's only field,
@@ -489,7 +524,9 @@ function and the user will be notified.
First, let's handle the errors in <code>renderTemplate</code>:
</p>
{{code "doc/articles/wiki/final-parsetemplate.go" `/^func renderTemplate/` `/^}/`}}
<pre>
!srcextract.bin -src=final-parsetemplate.go -name=renderTemplate
</pre>
<p>
The <code>http.Error</code> function sends a specified HTTP response code
@@ -501,7 +538,9 @@ Already the decision to put this in a separate function is paying off.
Now let's fix up <code>saveHandler</code>:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/^func saveHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=saveHandler
</pre>
<p>
Any errors that occur during <code>p.save()</code> will be reported
@@ -512,28 +551,35 @@ to the user.
<p>
There is an inefficiency in this code: <code>renderTemplate</code> calls
<code>ParseFiles</code> every time a page is rendered.
A better approach would be to call <code>ParseFiles</code> once at program
initialization, parsing all templates into a single <code>*Template</code>.
Then we can use the
<a href="/pkg/html/template/#Template.ExecuteTemplate"><code>ExecuteTemplate</code></a>
method to render a specific template.
<code>ParseFile</code> every time a page is rendered.
A better approach would be to call <code>ParseFile</code> once for each
template at program initialization, and store the resultant
<code>*Template</code> values in a data structure for later use.
</p>
<p>
First we create a global variable named <code>templates</code>, and initialize
it with <code>ParseFiles</code>.
First we create a global map named <code>templates</code> in which to store
our <code>*Template</code> values, keyed by <code>string</code>
(the template name):
</p>
{{code "doc/articles/wiki/final.go" `/var templates/`}}
<pre>
!srcextract.bin -src=final.go -name=templates
</pre>
<p>
The function <code>template.Must</code> is a convenience wrapper that panics
when passed a non-nil <code>error</code> value, and otherwise returns the
<code>*Template</code> unaltered. A panic is appropriate here; if the templates
can't be loaded the only sensible thing to do is exit the program.
Then we create an <code>init</code> function, which will be called before
<code>main</code> at program initialization. The function
<code>template.MustParseFile</code> is a convenience wrapper around
<code>ParseFile</code> that does not return an error code; instead, it panics
if an error is encountered. A panic is appropriate here; if the templates can't
be loaded the only sensible thing to do is exit the program.
</p>
<pre>
!srcextract.bin -src=final.go -name=init
</pre>
<p>
A <code>for</code> loop is used with a <code>range</code> statement to iterate
over an array constant containing the names of the templates we want parsed.
@@ -542,17 +588,13 @@ that array.
</p>
<p>
We then modify the <code>renderTemplate</code> function to call the
<code>templates.ExecuteTemplate</code> method with the name of the appropriate
template:
</p>
We then modify our <code>renderTemplate</code> function to call
the <code>Execute</code> method on the appropriate <code>Template</code> from
<code>templates</code>:
{{code "doc/articles/wiki/final.go" `/func renderTemplate/` `/^}/`}}
<p>
Note that the template name is the template file name, so we must
append <code>".html"</code> to the <code>tmpl</code> argument.
</p>
<pre>
!srcextract.bin -src=final.go -name=renderTemplate
</pre>
<h2>Validation</h2>
@@ -567,14 +609,17 @@ First, add <code>"regexp"</code> to the <code>import</code> list.
Then we can create a global variable to store our validation regexp:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/^var titleValidator/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=titleValidator
</pre>
<p>
The function <code>regexp.MustCompile</code> will parse and compile the
regular expression, and return a <code>regexp.Regexp</code>.
<code>MustCompile</code> is distinct from <code>Compile</code> in that it will
panic if the expression compilation fails, while <code>Compile</code> returns
an <code>error</code> as a second parameter.
<code>MustCompile</code>, like <code>template.MustParseFile</code>,
is distinct from <code>Compile</code> in that it will panic if
the expression compilation fails, while <code>Compile</code> returns an
<code>os.Error</code> as a second parameter.
</p>
<p>
@@ -582,7 +627,9 @@ Now, let's write a function that extracts the title string from the request
URL, and tests it against our <code>TitleValidator</code> expression:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/func getTitle/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=getTitle
</pre>
<p>
If the title is valid, it will be returned along with a <code>nil</code>
@@ -595,9 +642,13 @@ handler.
Let's put a call to <code>getTitle</code> in each of the handlers:
</p>
{{code "doc/articles/wiki/final-noclosure.go" `/^func viewHandler/` `/^}/`}}
{{code "doc/articles/wiki/final-noclosure.go" `/^func editHandler/` `/^}/`}}
{{code "doc/articles/wiki/final-noclosure.go" `/^func saveHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final-noclosure.go -name=viewHandler
!srcextract.bin -src=final-noclosure.go -name=editHandler
!srcextract.bin -src=final-noclosure.go -name=saveHandler
</pre>
<h2>Introducing Function Literals and Closures</h2>
@@ -605,7 +656,7 @@ Let's put a call to <code>getTitle</code> in each of the handlers:
Catching the error condition in each handler introduces a lot of repeated code.
What if we could wrap each of the handlers in a function that does this
validation and error checking? Go's
<a href="/ref/spec#Function_declarations">function
<a href="http://golang.org/doc/go_spec.html#Function_declarations">function
literals</a> provide a powerful means of abstracting functionality
that can help us here.
</p>
@@ -648,7 +699,9 @@ Now we can take the code from <code>getTitle</code> and use it here
(with some minor modifications):
</p>
{{code "doc/articles/wiki/final.go" `/func makeHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final.go -name=makeHandler
</pre>
<p>
The closure returned by <code>makeHandler</code> is a function that takes
@@ -669,16 +722,22 @@ Now we can wrap the handler functions with <code>makeHandler</code> in
package:
</p>
{{code "doc/articles/wiki/final.go" `/func main/` `/^}/`}}
<pre>
!srcextract.bin -src=final.go -name=main
</pre>
<p>
Finally we remove the calls to <code>getTitle</code> from the handler functions,
making them much simpler:
</p>
{{code "doc/articles/wiki/final.go" `/^func viewHandler/` `/^}/`}}
{{code "doc/articles/wiki/final.go" `/^func editHandler/` `/^}/`}}
{{code "doc/articles/wiki/final.go" `/^func saveHandler/` `/^}/`}}
<pre>
!srcextract.bin -src=final.go -name=viewHandler
!srcextract.bin -src=final.go -name=editHandler
!srcextract.bin -src=final.go -name=saveHandler
</pre>
<h2>Try it out!</h2>
@@ -691,8 +750,9 @@ Recompile the code, and run the app:
</p>
<pre>
$ go build wiki.go
$ ./wiki
$ 8g wiki.go
$ 8l wiki.8
$ ./8.out
</pre>
<p>

View File

@@ -1,6 +1,4 @@
<!--{
"Title": "Using Mercurial Queues with Codereview"
}-->
<!-- Using Mercurial Queues with Codereview -->
<h2 id="Introduction">Introduction</h2>

View File

@@ -45,7 +45,7 @@
turn.
</step>
<step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/true\n}/">
<step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/stay.*true\n}/">
Go functions can return multiple values.
<br/><br/>
@@ -82,6 +82,16 @@
associated with the current player.
</step>
<step title="Comparing functions" src="doc/codewalk/pig.go:/if action/,/currentPlayer\)\)\n\t\t}/">
Functions can be compared for equality in Go. From the
<a href="http://golang.org/doc/go_spec.html#Comparison_operators">language specification</a>:
Function values are equal if they refer to the same function or if both are <code>nil</code>.
<br/><br/>
We enforce that a <code>strategy</code> function can only return a legal
<code>action</code>: either <code>roll</code> or <code>stay</code>.
</step>
<step title="Simulating a tournament" src="doc/codewalk/pig.go:/\/\/ roundRobin/,/gamesPerStrategy\n}/">
The <code>roundRobin</code> function simulates a tournament and tallies wins.
Each strategy plays each other strategy <code>gamesPerSeries</code> times.

View File

@@ -1,130 +0,0 @@
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
/*
Generating random text: a Markov chain algorithm
Based on the program presented in the "Design and Implementation" chapter
of The Practice of Programming (Kernighan and Pike, Addison-Wesley 1999).
See also Computer Recreations, Scientific American 260, 122 - 125 (1989).
A Markov chain algorithm generates text by creating a statistical model of
potential textual suffixes for a given prefix. Consider this text:
I am not a number! I am a free man!
Our Markov chain algorithm would arrange this text into this set of prefixes
and suffixes, or "chain": (This table assumes a prefix length of two words.)
Prefix Suffix
"" "" I
"" I am
I am a
I am not
a free man!
am a free
am not a
a number! I
number! I am
not a number!
To generate text using this table we select an initial prefix ("I am", for
example), choose one of the suffixes associated with that prefix at random
with probability determined by the input statistics ("a"),
and then create a new prefix by removing the first word from the prefix
and appending the suffix (making the new prefix is "am a"). Repeat this process
until we can't find any suffixes for the current prefix or we exceed the word
limit. (The word limit is necessary as the chain table may contain cycles.)
Our version of this program reads text from standard input, parsing it into a
Markov chain, and writes generated text to standard output.
The prefix and output lengths can be specified using the -prefix and -words
flags on the command-line.
*/
package main
import (
"bufio"
"flag"
"fmt"
"io"
"math/rand"
"os"
"strings"
"time"
)
// Prefix is a Markov chain prefix of one or more words.
type Prefix []string
// String returns the Prefix as a string (for use as a map key).
func (p Prefix) String() string {
return strings.Join(p, " ")
}
// Shift removes the first word from the Prefix and appends the given word.
func (p Prefix) Shift(word string) {
copy(p, p[1:])
p[len(p)-1] = word
}
// Chain contains a map ("chain") of prefixes to a list of suffixes.
// A prefix is a string of prefixLen words joined with spaces.
// A suffix is a single word. A prefix can have multiple suffixes.
type Chain struct {
chain map[string][]string
prefixLen int
}
// NewChain returns a new Chain with prefixes of prefixLen words.
func NewChain(prefixLen int) *Chain {
return &Chain{make(map[string][]string), prefixLen}
}
// Build reads text from the provided Reader and
// parses it into prefixes and suffixes that are stored in Chain.
func (c *Chain) Build(r io.Reader) {
br := bufio.NewReader(r)
p := make(Prefix, c.prefixLen)
for {
var s string
if _, err := fmt.Fscan(br, &s); err != nil {
break
}
key := p.String()
c.chain[key] = append(c.chain[key], s)
p.Shift(s)
}
}
// Generate returns a string of at most n words generated from Chain.
func (c *Chain) Generate(n int) string {
p := make(Prefix, c.prefixLen)
var words []string
for i := 0; i < n; i++ {
choices := c.chain[p.String()]
if len(choices) == 0 {
break
}
next := choices[rand.Intn(len(choices))]
words = append(words, next)
p.Shift(next)
}
return strings.Join(words, " ")
}
func main() {
// Register command-line flags.
numWords := flag.Int("words", 100, "maximum number of words to print")
prefixLen := flag.Int("prefix", 2, "prefix length in words")
flag.Parse() // Parse command-line flags.
rand.Seed(time.Now().UnixNano()) // Seed the random number generator.
c := NewChain(*prefixLen) // Initialize a new Chain.
c.Build(os.Stdin) // Build chains from standard input.
text := c.Generate(*numWords) // Generate text.
fmt.Println(text) // Write text to standard output.
}

View File

@@ -1,307 +0,0 @@
<!--
Copyright 2011 The Go Authors. All rights reserved.
Use of this source code is governed by a BSD-style
license that can be found in the LICENSE file.
-->
<codewalk title="Generating arbitrary text: a Markov chain algorithm">
<step title="Introduction" src="doc/codewalk/markov.go:/Generating/,/line\./">
This codewalk describes a program that generates random text using
a Markov chain algorithm. The package comment describes the algorithm
and the operation of the program. Please read it before continuing.
</step>
<step title="Modeling Markov chains" src="doc/codewalk/markov.go:/ chain/">
A chain consists of a prefix and a suffix. Each prefix is a set
number of words, while a suffix is a single word.
A prefix can have an arbitrary number of suffixes.
To model this data, we use a <code>map[string][]string</code>.
Each map key is a prefix (a <code>string</code>) and its values are
lists of suffixes (a slice of strings, <code>[]string</code>).
<br/><br/>
Here is the example table from the package comment
as modeled by this data structure:
<pre>
map[string][]string{
" ": {"I"},
" I": {"am"},
"I am": {"a", "not"},
"a free": {"man!"},
"am a": {"free"},
"am not": {"a"},
"a number!": {"I"},
"number! I": {"am"},
"not a": {"number!"},
}</pre>
While each prefix consists of multiple words, we
store prefixes in the map as a single <code>string</code>.
It would seem more natural to store the prefix as a
<code>[]string</code>, but we can't do this with a map because the
key type of a map must implement equality (and slices do not).
<br/><br/>
Therefore, in most of our code we will model prefixes as a
<code>[]string</code> and join the strings together with a space
to generate the map key:
<pre>
Prefix Map key
[]string{"", ""} " "
[]string{"", "I"} " I"
[]string{"I", "am"} "I am"
</pre>
</step>
<step title="The Chain struct" src="doc/codewalk/markov.go:/type Chain/,/}/">
The complete state of the chain table consists of the table itself and
the word length of the prefixes. The <code>Chain</code> struct stores
this data.
</step>
<step title="The NewChain constructor function" src="doc/codewalk/markov.go:/func New/,/}/">
The <code>Chain</code> struct has two unexported fields (those that
do not begin with an upper case character), and so we write a
<code>NewChain</code> constructor function that initializes the
<code>chain</code> map with <code>make</code> and sets the
<code>prefixLen</code> field.
<br/><br/>
This is constructor function is not strictly necessary as this entire
program is within a single package (<code>main</code>) and therefore
there is little practical difference between exported and unexported
fields. We could just as easily write out the contents of this function
when we want to construct a new Chain.
But using these unexported fields is good practice; it clearly denotes
that only methods of Chain and its constructor function should access
those fields. Also, structuring <code>Chain</code> like this means we
could easily move it into its own package at some later date.
</step>
<step title="The Prefix type" src="doc/codewalk/markov.go:/type Prefix/">
Since we'll be working with prefixes often, we define a
<code>Prefix</code> type with the concrete type <code>[]string</code>.
Defining a named type clearly allows us to be explicit when we are
working with a prefix instead of just a <code>[]string</code>.
Also, in Go we can define methods on any named type (not just structs),
so we can add methods that operate on <code>Prefix</code> if we need to.
</step>
<step title="The String method" src="doc/codewalk/markov.go:/func[^\n]+String/,/}/">
The first method we define on <code>Prefix</code> is
<code>String</code>. It returns a <code>string</code> representation
of a <code>Prefix</code> by joining the slice elements together with
spaces. We will use this method to generate keys when working with
the chain map.
</step>
<step title="Building the chain" src="doc/codewalk/markov.go:/func[^\n]+Build/,/\n}/">
The <code>Build</code> method reads text from an <code>io.Reader</code>
and parses it into prefixes and suffixes that are stored in the
<code>Chain</code>.
<br/><br/>
The <code><a href="/pkg/io/#Reader">io.Reader</a></code> is an
interface type that is widely used by the standard library and
other Go code. Our code uses the
<code><a href="/pkg/fmt/#Fscan">fmt.Fscan</a></code> function, which
reads space-separated values from an <code>io.Reader</code>.
<br/><br/>
The <code>Build</code> method returns once the <code>Reader</code>'s
<code>Read</code> method returns <code>io.EOF</code> (end of file)
or some other read error occurs.
</step>
<step title="Buffering the input" src="doc/codewalk/markov.go:/bufio\.NewReader/">
This function does many small reads, which can be inefficient for some
<code>Readers</code>. For efficiency we wrap the provided
<code>io.Reader</code> with
<code><a href="/pkg/bufio/">bufio.NewReader</a></code> to create a
new <code>io.Reader</code> that provides buffering.
</step>
<step title="The Prefix variable" src="doc/codewalk/markov.go:/make\(Prefix/">
At the top of the function we make a <code>Prefix</code> slice
<code>p</code> using the <code>Chain</code>'s <code>prefixLen</code>
field as its length.
We'll use this variable to hold the current prefix and mutate it with
each new word we encounter.
</step>
<step title="Scanning words" src="doc/codewalk/markov.go:/var s string/,/\n }/">
In our loop we read words from the <code>Reader</code> into a
<code>string</code> variable <code>s</code> using
<code>fmt.Fscan</code>. Since <code>Fscan</code> uses space to
separate each input value, each call will yield just one word
(including punctuation), which is exactly what we need.
<br/><br/>
<code>Fscan</code> returns an error if it encounters a read error
(<code>io.EOF</code>, for example) or if it can't scan the requested
value (in our case, a single string). In either case we just want to
stop scanning, so we <code>break</code> out of the loop.
</step>
<step title="Adding a prefix and suffix to the chain" src="doc/codewalk/markov.go:/ key/,/key\], s\)">
The word stored in <code>s</code> is a new suffix. We add the new
prefix/suffix combination to the <code>chain</code> map by computing
the map key with <code>p.String</code> and appending the suffix
to the slice stored under that key.
<br/><br/>
The built-in <code>append</code> function appends elements to a slice
and allocates new storage when necessary. When the provided slice is
<code>nil</code>, <code>append</code> allocates a new slice.
This behavior conveniently ties in with the semantics of our map:
retrieving an unset key returns the zero value of the value type and
the zero value of <code>[]string</code> is <code>nil</code>.
When our program encounters a new prefix (yielding a <code>nil</code>
value in the map) <code>append</code> will allocate a new slice.
<br/><br/>
For more information about the <code>append</code> function and slices
in general see the
<a href="/doc/articles/slices_usage_and_internals.html">Slices: usage and internals</a> article.
</step>
<step title="Pushing the suffix onto the prefix" src="doc/codewalk/markov.go:/p\.Shift/">
Before reading the next word our algorithm requires us to drop the
first word from the prefix and push the current suffix onto the prefix.
<br/><br/>
When in this state
<pre>
p == Prefix{"I", "am"}
s == "not" </pre>
the new value for <code>p</code> would be
<pre>
p == Prefix{"am", "not"}</pre>
This operation is also required during text generation so we put
the code to perform this mutation of the slice inside a method on
<code>Prefix</code> named <code>Shift</code>.
</step>
<step title="The Shift method" src="doc/codewalk/markov.go:/func[^\n]+Shift/,/\n}/">
The <code>Shift</code> method uses the built-in <code>copy</code>
function to copy the last len(p)-1 elements of <code>p</code> to
the start of the slice, effectively moving the elements
one index to the left (if you consider zero as the leftmost index).
<pre>
p := Prefix{"I", "am"}
copy(p, p[:1])
// p == Prefix{"am", "am"}</pre>
We then assign the provided <code>word</code> to the last index
of the slice:
<pre>
// suffix == "not"
p[len(p)-1] = suffix
// p == Prefix{"am", "not"}</pre>
</step>
<step title="Generating text" src="doc/codewalk/markov.go:/func[^\n]+Generate/,/\n}/">
The <code>Generate</code> method is similar to <code>Build</code>
except that instead of reading words from a <code>Reader</code>
and storing them in a map, it reads words from the map and
appends them to a slice (<code>words</code>).
<br/><br/>
<code>Generate</code> uses a conditional for loop to generate
up to <code>n</code> words.
</step>
<step title="Getting potential suffixes" src="doc/codewalk/markov.go:/choices/,/}\n/">
At each iteration of the loop we retrieve a list of potential suffixes
for the current prefix. We access the <code>chain</code> map at key
<code>p.String()</code> and assign its contents to <code>choices</code>.
<br/><br/>
If <code>len(choices)</code> is zero we break out of the loop as there
are no potential suffixes for that prefix.
This test also works if the key isn't present in the map at all:
in that case, <code>choices</code> will be <code>nil</code> and the
length of a <code>nil</code> slice is zero.
</step>
<step title="Choosing a suffix at random" src="doc/codewalk/markov.go:/next := choices/,/Shift/">
To choose a suffix we use the
<code><a href="/pkg/rand/#Intn">rand.Intn</a></code> function.
It returns a random integer up to (but not including) the provided
value. Passing in <code>len(choices)</code> gives us a random index
into the full length of the list.
<br/><br/>
We use that index to pick our new suffix, assign it to
<code>next</code> and append it to the <code>words</code> slice.
<br/><br/>
Next, we <code>Shift</code> the new suffix onto the prefix just as
we did in the <code>Build</code> method.
</step>
<step title="Returning the generated text" src="doc/codewalk/markov.go:/Join\(words/">
Before returning the generated text as a string, we use the
<code>strings.Join</code> function to join the elements of
the <code>words</code> slice together, separated by spaces.
</step>
<step title="Command-line flags" src="doc/codewalk/markov.go:/Register command-line flags/,/prefixLen/">
To make it easy to tweak the prefix and generated text lengths we
use the <code><a href="/pkg/flag/">flag</a></code> package to parse
command-line flags.
<br/><br/>
These calls to <code>flag.Int</code> register new flags with the
<code>flag</code> package. The arguments to <code>Int</code> are the
flag name, its default value, and a description. The <code>Int</code>
function returns a pointer to an integer that will contain the
user-supplied value (or the default value if the flag was omitted on
the command-line).
</step>
<step title="Program set up" src="doc/codewalk/markov.go:/flag.Parse/,/rand.Seed/">
The <code>main</code> function begins by parsing the command-line
flags with <code>flag.Parse</code> and seeding the <code>rand</code>
package's random number generator with the current time.
<br/><br/>
If the command-line flags provided by the user are invalid the
<code>flag.Parse</code> function will print an informative usage
message and terminate the program.
</step>
<step title="Creating and building a new Chain" src="doc/codewalk/markov.go:/c := NewChain/,/c\.Build/">
To create the new <code>Chain</code> we call <code>NewChain</code>
with the value of the <code>prefix</code> flag.
<br/><br/>
To build the chain we call <code>Build</code> with
<code>os.Stdin</code> (which implements <code>io.Reader</code>) so
that it will read its input from standard input.
</step>
<step title="Generating and printing text" src="doc/codewalk/markov.go:/c\.Generate/,/fmt.Println/">
Finally, to generate text we call <code>Generate</code> with
the value of the <code>words</code> flag and assigning the result
to the variable <code>text</code>.
<br/><br/>
Then we call <code>fmt.Println</code> to write the text to standard
output, followed by a carriage return.
</step>
<step title="Using this program" src="doc/codewalk/markov.go">
To use this program, first build it with the
<a href="/cmd/go/">go</a> command:
<pre>
$ go build markov.go</pre>
And then execute it while piping in some input text:
<pre>
$ echo "a man a plan a canal panama" \
| ./markov -prefix=1
a plan a man a plan a canal panama</pre>
Here's a transcript of generating some text using the Go distribution's
README file as source material:
<pre>
$ ./markov -words=10 &lt $GOROOT/go/README
This is the source code repository for the Go source
$ ./markov -prefix=1 -words=10 &lt $GOROOT/go/README
This is the go directory (the one containing this README).
$ ./markov -prefix=1 -words=10 &lt $GOROOT/go/README
This is the variable if you have just untarred a</pre>
</step>
<step title="An exercise for the reader" src="doc/codewalk/markov.go">
The <code>Generate</code> function does a lot of allocations when it
builds the <code>words</code> slice. As an exercise, modify it to
take an <code>io.Writer</code> to which it incrementally writes the
generated text with <code>Fprint</code>.
Aside from being more efficient this makes <code>Generate</code>
more symmetrical to <code>Build</code>.
</step>
</codewalk>

View File

@@ -6,7 +6,7 @@ package main
import (
"fmt"
"math/rand"
"rand"
)
const (
@@ -61,6 +61,9 @@ func play(strategy0, strategy1 strategy) int {
currentPlayer := rand.Intn(2) // Randomly decide who plays first
for s.player+s.thisTurn < win {
action := strategies[currentPlayer](s)
if action != roll && action != stay {
panic(fmt.Sprintf("Player %d is cheating", currentPlayer))
}
s, turnIsOver = action(s)
if turnIsOver {
currentPlayer = (currentPlayer + 1) % 2

View File

@@ -65,7 +65,7 @@ and then loops passing completed Resources back to the pending
channel after appropriate delays.
</step>
<step title="Creating channels" src="doc/codewalk/urlpoll.go:/Create our/,/complete/">
<step title="Creating channels" src="doc/codewalk/urlpoll.go:/create our/,/complete/">
First, main makes two channels of *Resource, pending and complete.
<br/><br/>
Inside main, a new goroutine sends one Resource per URL to pending
@@ -75,7 +75,7 @@ The pending and complete channels are passed to each of the Poller
goroutines, within which they are known as in and out.
</step>
<step title="Initializing StateMonitor" src="doc/codewalk/urlpoll.go:/Launch the StateMonitor/,/statusInterval/">
<step title="Initializing StateMonitor" src="doc/codewalk/urlpoll.go:/launch the StateMonitor/,/statusInterval/">
StateMonitor will initialize and launch a goroutine that stores the state
of each Resource. We will look at this function in detail later.
<br/><br/>
@@ -83,14 +83,14 @@ For now, the important thing to note is that it returns a channel of State,
which is saved as status and passed to the Poller goroutines.
</step>
<step title="Launching Poller goroutines" src="doc/codewalk/urlpoll.go:/Launch some Poller/,/}/">
<step title="Launching Poller goroutines" src="doc/codewalk/urlpoll.go:/launch some Poller/,/}/">
Now that it has the necessary channels, main launches a number of
Poller goroutines, passing the channels as arguments.
The channels provide the means of communication between the main, Poller, and
StateMonitor goroutines.
</step>
<step title="Send Resources to pending" src="doc/codewalk/urlpoll.go:/Send some Resources/,/}\(\)/">
<step title="Send Resources to pending" src="doc/codewalk/urlpoll.go:/send some Resources/,/}\(\)/">
To add the initial work to the system, main starts a new goroutine
that allocates and sends one Resource per URL to pending.
<br/><br/>

View File

@@ -5,16 +5,17 @@
package main
import (
"http"
"log"
"net/http"
"time"
)
const (
numPollers = 2 // number of Poller goroutines to launch
pollInterval = 60 * time.Second // how often to poll each URL
statusInterval = 10 * time.Second // how often to log status to stdout
errTimeout = 10 * time.Second // back-off timeout on error
numPollers = 2 // number of Poller goroutines to launch
second = 1e9 // one second is 1e9 nanoseconds
pollInterval = 60 * second // how often to poll each URL
statusInterval = 10 * second // how often to log status to stdout
errTimeout = 10 * second // back-off timeout on error
)
var urls = []string{
@@ -32,7 +33,7 @@ type State struct {
// StateMonitor maintains a map that stores the state of the URLs being
// polled, and prints the current state every updateInterval nanoseconds.
// It returns a chan State to which resource state should be sent.
func StateMonitor(updateInterval time.Duration) chan<- State {
func StateMonitor(updateInterval int64) chan<- State {
updates := make(chan State)
urlStatus := make(map[string]string)
ticker := time.NewTicker(updateInterval)
@@ -60,7 +61,7 @@ func logState(s map[string]string) {
// Resource represents an HTTP URL to be polled by this program.
type Resource struct {
url string
errCount int
errCount int64
}
// Poll executes an HTTP HEAD request for url
@@ -70,7 +71,7 @@ func (r *Resource) Poll() string {
if err != nil {
log.Println("Error", r.url, err)
r.errCount++
return err.Error()
return err.String()
}
r.errCount = 0
return resp.Status
@@ -78,8 +79,8 @@ func (r *Resource) Poll() string {
// Sleep sleeps for an appropriate interval (dependant on error state)
// before sending the Resource to done.
func (r *Resource) Sleep(done chan<- *Resource) {
time.Sleep(pollInterval + errTimeout*time.Duration(r.errCount))
func (r *Resource) Sleep(done chan *Resource) {
time.Sleep(pollInterval + errTimeout*r.errCount)
done <- r
}
@@ -92,18 +93,18 @@ func Poller(in <-chan *Resource, out chan<- *Resource, status chan<- State) {
}
func main() {
// Create our input and output channels.
// create our input and output channels
pending, complete := make(chan *Resource), make(chan *Resource)
// Launch the StateMonitor.
// launch the StateMonitor
status := StateMonitor(statusInterval)
// Launch some Poller goroutines.
// launch some Poller goroutines
for i := 0; i < numPollers; i++ {
go Poller(pending, complete, status)
}
// Send some Resources to the pending queue.
// send some Resources to the pending queue
go func() {
for _, url := range urls {
pending <- &Resource{url: url}

53
doc/community.html Normal file
View File

@@ -0,0 +1,53 @@
<!-- title Community -->
<div class="left-column">
<h2 id="developer_info">The Go Community</h2>
<h3 id="mailinglist"><a href="http://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
mailing list is for general Go discussion.</p>
<h3 id=""><a href="http://godashboard.appspot.com/package">Go Packages Dashboard</a></h3>
<p>A list of the most popular <a href="/cmd/goinstall/">goinstall</a>'d
Go libraries.</p>
<h3 id=""><a href="http://godashboard.appspot.com/project">Go Project Dashboard</a></h3>
<p>A list of external Go projects including programs and libraries.</p>
<h3 id="irc"><a href="irc:irc.freenode.net/go-nuts">Go IRC Channel</a></h3>
<p><b>#go-nuts</b> on <b>irc.freenode.net</b> is the official Go IRC channel.</p>
<h3 id="twitter"><a href="http://twitter.com/go_nuts">@go_nuts at Twitter</a></h3>
<p>The Go project's official Twitter account.</p>
</div>
<div class="right-column">
<h2 id="blogs">Blogs</h2>
<h3 id="blog_go"><a href="http://blog.golang.org/">The Go Blog</a></h3>
<p>
The Go project's official blog, maintained by the core Go developers.
</p>
<h3 id="blog_rsc"><a href="http://research.swtch.com/search/label/Go">research!rsc</a></h3>
<p>
Posts labelled 'Go' by Russ Cox, one of the core Go developers.
</p>
<h3 id="blog_iant"><a href="http://www.airs.com/blog/archives/category/programming">Airs</a></h3>
<p>
Posts labelled 'Programming' by Ian Lance Taylor, one of the core Go developers.
</p>
<h3 id="blog_adg"><a href="http://nf.id.au/tag/go">nf.id.au</a></h3>
<p>
Posts labelled 'Go' by Andrew Gerrand, one of the core Go developers.
</p>
</div>
<div class="end-columns"></div>

View File

@@ -1,59 +1,10 @@
<!--{
"Title": "The Go Project",
"Path": "/project/"
}-->
<img class="gopher" src="/doc/gopher/project.png" />
<div id="manual-nav"></div>
<p>
Go is an open source project developed by a team at
<a href="http://google.com/">Google</a> and many
<a href="/CONTRIBUTORS">contributors</a> from the open source community.
</p>
<p>
Go is distributed under a <a href="/LICENSE">BSD-style license</a>.
</p>
<h3 id="announce"><a href="http://groups.google.com/group/golang-announce">Announcements Mailing List</a></h3>
<p>
A low traffic mailing list for important announcements, such as new releases.
</p>
<p>
We encourage all Go users to subscribe to
<a href="http://groups.google.com/group/golang-announce">golang-announce</a>.
</p>
<h2 id="resources">Developer Resources</h2>
<h3 id="source"><a href="https://code.google.com/p/go/source">Source Code</a></h3>
<p>Check out the Go source code.</p>
<h3 id="release"><a href="/doc/devel/release.html">Release History</a></h3>
<p>A summary of the changes between Go releases.</p>
<h3 id="weekly"><a href="/doc/devel/weekly.html">Weekly Snapshot History</a></h3>
<p>A summary of the changes between weekly snapshots of Go.</p>
<h3 id="golang-dev"><a href="http://groups.google.com/group/golang-dev">Developer Mailing List</a></h3>
<p>The <a href="http://groups.google.com/group/golang-dev">golang-dev</a>
mailing list is for discussing and reviewing code for the Go project.</p>
<p>For general discussion of Go programming, see <a
href="http://groups.google.com/group/golang-nuts">golang-nuts</a>.</p>
<h3 id="golang-checkins"><a href="http://groups.google.com/group/golang-checkins">Checkins Mailing List</a></h3>
<p>A mailing list that receives a message summarizing each checkin to the Go repository.</p>
<h3 id="build_status"><a href="http://build.golang.org/">Build Status</a></h3>
<p>View the status of Go builds across the supported operating
systems and architectures.</p>
<!-- title Contributing -->
<div class="left-column">
<h2 id="howto">How you can help</h2>
<h3><a href="http://code.google.com/p/go/issues">Reporting issues</a></h3>
<h3>Reporting issues</h3>
<p>
If you spot bugs, mistakes, or inconsistencies in the Go project's code or
@@ -68,13 +19,13 @@ a new one.)
We pride ourselves on being meticulous; no issue is too small.
</p>
<h3><a href="/doc/contribute.html">Contributing code</a></h3>
<h3>Contributing code</h3>
<p>
Go is an open source project and we welcome contributions from the community.
</p>
<p>
To get started, read these <a href="/doc/contribute.html">contribution
To get started, read these <a href="contribute.html">contribution
guidelines</a> for information on design, testing, and our code review process.
</p>
<p>
@@ -84,25 +35,32 @@ open issues that interest you. Those labeled
are particularly in need of outside help.
</p>
</div>
<h2 id="community">The Go Community</h2>
<div class="right-column">
<h3 id="mailinglist"><a href="http://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
mailing list is for general Go discussion.</p>
<h2 id="">The Go Project</h2>
<h3 id="projects"><a href="http://godashboard.appspot.com/project">Go Project Dashboard</a></h3>
<p>A list of external Go projects including programs and libraries.</p>
<h3 id="build_status"><a href="http://godashboard.appspot.com/">Build Status</a></h3>
<p>View the status of Go builds across the supported operating
systems and architectures.</p>
<h3 id="irc"><a href="irc:irc.freenode.net/go-nuts">Go IRC Channel</a></h3>
<p><b>#go-nuts</b> on <b>irc.freenode.net</b> is the official Go IRC channel.</p>
<h3 id="roadmap"><a href="devel/roadmap.html">Roadmap</a></h3>
<p>Features and ideas being developed or discussed by the Go team.</p>
<h3 id="plus"><a href="https://plus.google.com/101406623878176903605/posts">The Go Programming Language at Google+</a></h3>
<p>The Go project's Google+ page.</p>
<h3 id="release"><a href="devel/release.html">Release History</a></h3>
<p>A summary of the changes between tagged releases of Go.</p>
<h3 id="twitter"><a href="http://twitter.com/go_nuts">@go_nuts at Twitter</a></h3>
<p>The Go project's official Twitter account.</p>
<h3 id="golang-dev"><a href="http://groups.google.com/group/golang-dev">Developer Mailing List</a></h3>
<p>The <a href="http://groups.google.com/group/golang-dev">golang-dev</a>
mailing list is for discussing and reviewing code for the Go project.</p>
<p>For general discussion of Go programming, see <a
href="http://groups.google.com/group/golang-nuts">golang-nuts</a>.</p>
<h3 id="golang-checkins"><a href="http://groups.google.com/group/golang-checkins">Checkins Mailing List</a></h3>
<p>A mailing list that receives a message summarizing each checkin to the Go repository.</p>
</div>
<div class="end-columns"></div>
<h3 id="blog"><a href="http://blog.golang.org/">The Go Blog</a></h3>
<p>The official blog of the Go project, featuring news and in-depth articles by
the Go team and guests.</p>

View File

@@ -1,13 +1,11 @@
<!--{
"Title": "Contribution Guidelines"
}-->
<!-- Contribution Guidelines -->
<h2 id="Introduction">Introduction</h2>
<p>
This document explains how to contribute changes to the Go project.
It assumes you have installed Go using the
<a href="/doc/install">installation instructions</a> and
<a href="install.html">installation instructions</a> and
have <a href="code.html">written and tested your code</a>.
(Note that the <code>gccgo</code> frontend lives elsewhere;
see <a href="gccgo_contribute.html">Contributing to gccgo</a>.)
@@ -211,11 +209,10 @@ The <code>Reviewer</code> line lists the reviewers assigned
to this change, and the <code>CC</code> line lists people to
notify about the change.
These can be code review nicknames or arbitrary email addresses.
Unless explicitly told otherwise, such as in the discussion leading
up to sending in the change list, leave the reviewer field blank.
This means that the
If you don't know who is best to review the change, set the
reviewer field to the
<a href="http://groups.google.com/group/golang-dev">golang-dev@googlegroups.com</a>
mailing list will be used as the reviewer.
mailing list.
</p>
<p>
@@ -404,7 +401,7 @@ $ hg mail -r golang-dev@googlegroups.com --cc math-nuts@swtch.com 99999
<p>
Running <code>hg mail</code> will send an email to you and the reviewers
asking them to visit the issue's URL and make comments on the change.
asking them to visit the issue's URL and make coments on the change.
When done, the reviewer clicks &ldquo;Publish and Mail comments&rdquo;
to send comments back.
</p>
@@ -525,7 +522,7 @@ This rigmarole needs to be done only for your first submission.
<p>Code that you contribute should use the standard copyright header:</p>
<pre>
// Copyright 2012 The Go Authors. All rights reserved.
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
</pre>

View File

@@ -1,483 +0,0 @@
<!--{
"Title": "Debugging Go Code with GDB",
"Path": "/doc/gdb"
}-->
<p><i>
This applies to the <code>gc</code> toolchain. Gccgo has native gdb support.
Besides this overview you might want to consult the
<a href="http://sourceware.org/gdb/current/onlinedocs/gdb/">GDB manual</a>.
</i></p>
<h2 id="Introduction">Introduction</h2>
<p>
When you compile and link your Go programs with the <code>gc</code> toolchain
on Linux, Mac OS X or FreeBSD, the resulting binaries contain DWARFv3
debugging information that recent versions (&gt;7.1) of the GDB debugger can
use to inspect a live process or a core dump.
</p>
<p>
Pass the <code>'-s'</code> flag to the linker to omit the debug information
(for example, <code>go build -ldflags "-s" prog.go</code>).
</p>
<h3 id="Common_Operations">Common Operations</h3>
<ul>
<li>
Show file and line number for code
, set breakpoints and disassemble:
<pre>(gdb) <b>list</b>
(gdb) <b>list <i>line</i></b>
(gdb) <b>list <i>file.go</i>:<i>line</i></b>
(gdb) <b>break <i>line</i></b>
(gdb) <b>break <i>file.go</i>:<i>line</i></b>
(gdb) <b>disas</b></pre>
</li>
<li>
Show backtraces and unwind stack frames:
<pre>(gdb) <b>bt</b>
(gdb) <b>frame <i>n</i></b></pre>
</li>
<li>
Show the name, type and location on the stack frame of local variables,
arguments and return values:
<pre>(gdb) <b>info locals</b>
(gdb) <b>info args</b>
(gdb) <b>p variable</b>
(gdb) <b>whatis variable</b></pre>
</li>
<li>
Show the name, type and location of global variables:
<pre>(gdb) <b>info variables <i>regexp</i></b></pre>
</li>
</ul>
<h3 id="Go_Extensions">Go Extensions</h3>
<p>
A recent extension mechanism to GDB allows it to load extension scripts for a
given binary. The tool chain uses this to extend GDB with a handful of
commands to inspect internals of the runtime code (such as goroutines) and to
pretty print the built-in map, slice and channel types.
</p>
<ul>
<li>
Pretty printing a string, slice, map, channel or interface:
<pre>(gdb) <b>p <i>var</i></b></pre>
</li>
<li>
A $len() and $cap() function for strings, slices and maps:
<pre>(gdb) <b>p $len(<i>var</i>)</b></pre>
</li>
<li>
A function to cast interfaces to their dynamic types:
<pre>(gdb) <b>p $dtype(<i>var</i>)</b>
(gdb) <b>iface <i>var</i></b></pre>
<p class="detail"><b>Known issue:</b> GDB cant automatically find the dynamic
type of an interface value if its long name differs from its short name
(annoying when printing stacktraces, the pretty printer falls back to printing
the short type name and a pointer).</p>
</li>
<li>
Inspecting goroutines:
<pre>(gdb) <b>info goroutines</b>
(gdb) <b>goroutine <i>n</i> <i>cmd</i></b>
(gdb) <b>help goroutine</b></pre>
For example:
<pre>(gdb) <b>goroutine 12 bt</b></pre>
</li>
</ul>
<p>
If you'd like to see how this works, or want to extend it, take a look at <a
href="/src/pkg/runtime/runtime-gdb.py">src/pkg/runtime/runtime-gdb.py</a> in
the Go source distribution. It depends on some special magic types
(<code>hash&lt;T,U&gt;</code>) and variables (<code>runtime.m</code> and
<code>runtime.g</code>) that the linker
(<a href="/src/cmd/ld/dwarf.c">src/cmd/ld/dwarf.c</a>) ensures are described in
the DWARF code.
</p>
<p>
If you're interested in what the debugging information looks like, run
'<code>objdump -W 6.out</code>' and browse through the <code>.debug_*</code>
sections.
</p>
<h3 id="Known_Issues">Known Issues</h3>
<ol>
<li>String pretty printing only triggers for type string, not for types derived
from it.</li>
<li>Type information is missing for the C parts of the runtime library.</li>
<li>GDB does not understand Gos name qualifications and treats
<code>"fmt.Print"</code> as an unstructured literal with a <code>"."</code>
that needs to be quoted. It objects even more strongly to method names of
the form <code>pkg.(*MyType).Meth</code>.
<li>All global variables are lumped into package <code>"main"</code>.</li>
</ol>
<h2 id="Tutorial">Tutorial</h2>
<p>
In this tutorial we will inspect the binary of the
<a href="/pkg/regexp/">regexp</a> package's unit tests. To build the binary,
change to <code>$GOROOT/src/pkg/regexp</code> and run <code>go test -c</code>.
This should produce an executable file named <code>regexp.test</code>.
</p>
<h3 id="Getting_Started">Getting Started</h3>
<p>
Launch GDB, debugging <code>regexp.test</code>:
</p>
<pre>
$ <b>gdb regexp.test</b>
GNU gdb (GDB) 7.2-gg8
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv 3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
Type "show copying" and "show warranty" for licensing/warranty details.
This GDB was configured as "x86_64-linux".
Reading symbols from /home/user/go/src/pkg/regexp/regexp.test...
done.
Loading Go Runtime support.
(gdb)
</pre>
<p>
The message <code>"Loading Go Runtime support"</code> means that GDB loaded the
extension from <code>$GOROOT/src/pkg/runtime/runtime-gdb.py</code>.
</p>
<p>
To help GDB find the Go runtime sources and the accompanying support script,
pass your <code>$GOROOT</code> with the <code>'-d'</code> flag:
</p>
<pre>
$ <b>gdb regexp.test -d $GOROOT</b>
</pre>
<p>
If for some reason GDB still can't find that directory or that script, you can load
it by hand by telling gdb (assuming you have the go sources in
<code>~/go/</code>):
<p>
<pre>
(gdb) <b>source ~/go/src/pkg/runtime/runtime-gdb.py</b>
Loading Go Runtime support.
</pre>
<h3 id="Inspecting_the_source">Inspecting the source</h3>
<p>
Use the <code>"l"</code> or <code>"list"</code> command to inspect source code.
</p>
<pre>
(gdb) <b>l</b>
</pre>
<p>
List a specific part of the source parametrizing <code>"list"</code> with a
function name (it must be qualified with its package name).
</p>
<pre>
(gdb) <b>l main.main</b>
</pre>
<p>
List a specific file and line number:
</p>
<pre>
(gdb) <b>l regexp.go:1</b>
(gdb) <i># Hit enter to repeat last command. Here, this lists next 10 lines.</i>
</pre>
<h3 id="Naming">Naming</h3>
<p>
Variable and function names must be qualified with the name of the packages
they belong to. The <code>Compile</code> function from the <code>regexp</code>
package is known to GDB as <code>'regexp.Compile'</code>.
</p>
<p>
Methods must be qualified with the name of their receiver types. For example,
the <code>*Regexp</code> types <code>String</code> method is known as
<code>'regexp.(*Regexp).String'</code>.
</p>
<p>
Variables that shadow other variables are magically suffixed with a number in the debug info.
Variables referenced by closures will appear as pointers magically prefixed with '&amp;'.
</p>
<h3 id="Setting_breakpoints">Setting breakpoints</h3>
<p>
Set a breakpoint at the <code>TestFind</code> function:
</p>
<pre>
(gdb) <b>b 'regexp.TestFind'</b>
Breakpoint 1 at 0x424908: file /home/user/go/src/pkg/regexp/find_test.go, line 148.
</pre>
<p>
Run the program:
</p>
<pre>
(gdb) <b>run</b>
Starting program: /home/user/go/src/pkg/regexp/regexp.test
Breakpoint 1, regexp.TestFind (t=0xf8404a89c0) at /home/user/go/src/pkg/regexp/find_test.go:148
148 func TestFind(t *testing.T) {
</pre>
<p>
Execution has paused at the breakpoint.
See which goroutines are running, and what they're doing:
</p>
<pre>
(gdb) <b>info goroutines</b>
1 waiting runtime.gosched
* 13 running runtime.goexit
</pre>
<p>
the one marked with the <code>*</code> is the current goroutine.
</p>
<h3 id="Inspecting_the_stack">Inspecting the stack</h3>
<p>
Look at the stack trace for where weve paused the program:
</p>
<pre>
(gdb) <b>bt</b> <i># backtrace</i>
#0 regexp.TestFind (t=0xf8404a89c0) at /home/user/go/src/pkg/regexp/find_test.go:148
#1 0x000000000042f60b in testing.tRunner (t=0xf8404a89c0, test=0x573720) at /home/user/go/src/pkg/testing/testing.go:156
#2 0x000000000040df64 in runtime.initdone () at /home/user/go/src/pkg/runtime/proc.c:242
#3 0x000000f8404a89c0 in ?? ()
#4 0x0000000000573720 in ?? ()
#5 0x0000000000000000 in ?? ()
</pre>
<p>
The other goroutine, number 1, is stuck in <code>runtime.gosched</code>, blocked on a channel receive:
</p>
<pre>
(gdb) <b>goroutine 1 bt</b>
#0 0x000000000040facb in runtime.gosched () at /home/user/go/src/pkg/runtime/proc.c:873
#1 0x00000000004031c9 in runtime.chanrecv (c=void, ep=void, selected=void, received=void)
at /home/user/go/src/pkg/runtime/chan.c:342
#2 0x0000000000403299 in runtime.chanrecv1 (t=void, c=void) at/home/user/go/src/pkg/runtime/chan.c:423
#3 0x000000000043075b in testing.RunTests (matchString={void (struct string, struct string, bool *, error *)}
0x7ffff7f9ef60, tests= []testing.InternalTest = {...}) at /home/user/go/src/pkg/testing/testing.go:201
#4 0x00000000004302b1 in testing.Main (matchString={void (struct string, struct string, bool *, error *)}
0x7ffff7f9ef80, tests= []testing.InternalTest = {...}, benchmarks= []testing.InternalBenchmark = {...})
at /home/user/go/src/pkg/testing/testing.go:168
#5 0x0000000000400dc1 in main.main () at /home/user/go/src/pkg/regexp/_testmain.go:98
#6 0x00000000004022e7 in runtime.mainstart () at /home/user/go/src/pkg/runtime/amd64/asm.s:78
#7 0x000000000040ea6f in runtime.initdone () at /home/user/go/src/pkg/runtime/proc.c:243
#8 0x0000000000000000 in ?? ()
</pre>
<p>
The stack frame shows were currently executing the <code>regexp.TestFind</code> function, as expected.
</p>
<pre>
(gdb) <b>info frame</b>
Stack level 0, frame at 0x7ffff7f9ff88:
rip = 0x425530 in regexp.TestFind (/home/user/go/src/pkg/regexp/find_test.go:148);
saved rip 0x430233
called by frame at 0x7ffff7f9ffa8
source language minimal.
Arglist at 0x7ffff7f9ff78, args: t=0xf840688b60
Locals at 0x7ffff7f9ff78, Previous frame's sp is 0x7ffff7f9ff88
Saved registers:
rip at 0x7ffff7f9ff80
</pre>
<p>
The command <code>info locals</code> lists all variables local to the function and their values, but is a bit
dangerous to use, since it will also try to print uninitialized variables. Uninitialized slices may cause gdb to try
to print arbitrary large arrays.
</p>
<p>
The functions arguments:
</p>
<pre>
(gdb) <b>info args</b>
t = 0xf840688b60
</pre>
<p>
When printing the argument, notice that its a pointer to a
<code>Regexp</code> value. Note that GDB has incorrectly put the <code>*</code>
on the right-hand side of the type name and made up a 'struct' keyword, in traditional C style.
</p>
<pre>
(gdb) <b>p re</b>
(gdb) p t
$1 = (struct testing.T *) 0xf840688b60
(gdb) p t
$1 = (struct testing.T *) 0xf840688b60
(gdb) p *t
$2 = {errors = "", failed = false, ch = 0xf8406f5690}
(gdb) p *t-&gt;ch
$3 = struct hchan&lt;*testing.T&gt;
</pre>
<p>
That <code>struct hchan&lt;*testing.T&gt;</code> is the runtime-internal representation of a channel. It is currently empty, or gdb would have pretty-printed it's contents.
</p>
<p>
Stepping forward:
</p>
<pre>
(gdb) <b>n</b> <i># execute next line</i>
149 for _, test := range findTests {
(gdb) <i># enter is repeat</i>
150 re := MustCompile(test.pat)
(gdb) <b>p test.pat</b>
$4 = ""
(gdb) <b>p re</b>
$5 = (struct regexp.Regexp *) 0xf84068d070
(gdb) <b>p *re</b>
$6 = {expr = "", prog = 0xf840688b80, prefix = "", prefixBytes = []uint8, prefixComplete = true,
prefixRune = 0, cond = 0 '\000', numSubexp = 0, longest = false, mu = {state = 0, sema = 0},
machine = []*regexp.machine}
(gdb) <b>p *re->prog</b>
$7 = {Inst = []regexp/syntax.Inst = {{Op = 5 '\005', Out = 0, Arg = 0, Rune = []int}, {Op =
6 '\006', Out = 2, Arg = 0, Rune = []int}, {Op = 4 '\004', Out = 0, Arg = 0, Rune = []int}},
Start = 1, NumCap = 2}
</pre>
<p>
We can step into the <code>String</code>function call with <code>"s"</code>:
</p>
<pre>
(gdb) <b>s</b>
regexp.(*Regexp).String (re=0xf84068d070, noname=void) at /home/user/go/src/pkg/regexp/regexp.go:97
97 func (re *Regexp) String() string {
</pre>
<p>
Get a stack trace to see where we are:
</p>
<pre>
(gdb) <b>bt</b>
#0 regexp.(*Regexp).String (re=0xf84068d070, noname=void)
at /home/user/go/src/pkg/regexp/regexp.go:97
#1 0x0000000000425615 in regexp.TestFind (t=0xf840688b60)
at /home/user/go/src/pkg/regexp/find_test.go:151
#2 0x0000000000430233 in testing.tRunner (t=0xf840688b60, test=0x5747b8)
at /home/user/go/src/pkg/testing/testing.go:156
#3 0x000000000040ea6f in runtime.initdone () at /home/user/go/src/pkg/runtime/proc.c:243
....
</pre>
<p>
Look at the source code:
</p>
<pre>
(gdb) <b>l</b>
92 mu sync.Mutex
93 machine []*machine
94 }
95
96 // String returns the source text used to compile the regular expression.
97 func (re *Regexp) String() string {
98 return re.expr
99 }
100
101 // Compile parses a regular expression and returns, if successful,
</pre>
<h3 id="Pretty_Printing">Pretty Printing</h3>
<p>
GDB's pretty printing mechanism is triggered by regexp matches on type names. An example for slices:
</p>
<pre>
(gdb) <b>p utf</b>
$22 = []uint8 = {0 '\000', 0 '\000', 0 '\000', 0 '\000'}
</pre>
<p>
Since slices, arrays and strings are not C pointers, GDB can't interpret the subscripting operation for you, but
you can look inside the runtime representation to do that (tab completion helps here):
</p>
<pre>
(gdb) <b>p slc</b>
$11 = []int = {0, 0}
(gdb) <b>p slc-&gt;</b><i>&lt;TAB&gt;</i>
array slc len
(gdb) <b>p slc->array</b>
$12 = (int *) 0xf84057af00
(gdb) <b>p slc->array[1]</b>
$13 = 0</pre>
<p>
The extension functions $len and $cap work on strings, arrays and slices:
</p>
<pre>
(gdb) <b>p $len(utf)</b>
$23 = 4
(gdb) <b>p $cap(utf)</b>
$24 = 4
</pre>
<p>
Channels and maps are 'reference' types, which gdb shows as pointers to C++-like types <code>hash&lt;int,string&gt;*</code>. Dereferencing will trigger prettyprinting
</p>
<p>
Interfaces are represented in the runtime as a pointer to a type descriptor and a pointer to a value. The Go GDB runtime extension decodes this and automatically triggers pretty printing for the runtime type. The extension function <code>$dtype</code> decodes the dynamic type for you (examples are taken from a breakpoint at <code>regexp.go</code> line 293.)
</p>
<pre>
(gdb) <b>p i</b>
$4 = {str = "cbb"}
(gdb) <b>whatis i</b>
type = regexp.input
(gdb) <b>p $dtype(i)</b>
$26 = (struct regexp.inputBytes *) 0xf8400b4930
(gdb) <b>iface i</b>
regexp.input: struct regexp.inputBytes *
</pre>

11
doc/devel/index.html Normal file
View File

@@ -0,0 +1,11 @@
<!-- The Go project -->
<ul>
<li><a href="roadmap.html">Roadmap</a></li>
<li><a href="release.html">Release history</a></li>
<li><a href="weekly.html">Weekly snapshot history</a></li>
<li><a href="http://godashboard.appspot.com">Build and benchmark status</a></li>
</ul>
<ul>
<li><a href="../contribute.html">Contributing code</a></li>
</ul>

View File

@@ -1,6 +1,4 @@
<!--{
"Title": "Release History"
}-->
<!-- Release History -->
<p>This page summarizes the changes between official stable releases of Go.
Between releases we issue less stable
@@ -13,316 +11,9 @@ has full details.</p>
<pre>
hg pull
hg update <i>tag</i>
hg update release.r<i>NN</i>
</pre>
<h2 id="go1">go1 (released 2012/03/28)</h2>
<p>
Go 1 is a major release of Go that will be stable in the long term.
Read the <a href="/doc/go1.html">Go 1 Release Notes</a> for more information.
</p>
<p>
It is intended that programs written for Go 1 will continue to compile and run
correctly, unchanged, under future versions of Go 1.
Read the <a href="/doc/go1compat.html">Go 1 compatibility document</a> for more
about the future of Go 1.
</p>
<p>
The go1 release corresponds to
<code><a href="weekly.html#2012-03-27">weekly.2012-03-27</a></code>.
</p>
<h2 id="r60">r60 (released 2011/09/07)</h2>
<p>
The r60 release corresponds to
<code><a href="weekly.html#2011-08-17">weekly.2011-08-17</a></code>.
This section highlights the most significant changes in this release.
For a more detailed summary, see the
<a href="weekly.html#2011-08-17">weekly release notes</a>.
For complete information, see the
<a href="http://code.google.com/p/go/source/list?r=release-branch.r60">Mercurial change list</a>.
</p>
<h3 id="r60.lang">Language</h3>
<p>
An "else" block is now required to have braces except if the body of the "else"
is another "if". Since gofmt always puts those braces in anyway,
gofmt-formatted programs will not be affected.
To fix other programs, run gofmt.
</p>
<h3 id="r60.pkg">Packages</h3>
<p>
<a href="/pkg/http/">Package http</a>'s URL parsing and query escaping code
(such as <code>ParseURL</code> and <code>URLEscape</code>) has been moved to
the new <a href="/pkg/url/">url package</a>, with several simplifications to
the names. Client code can be updated automatically with gofix.
</p>
<p>
<a href="/pkg/image/">Package image</a> has had significant changes made to the
<code>Pix</code> field of struct types such as
<a href="/pkg/image/#RGBA">image.RGBA</a> and
<a href="/pkg/image/#NRGBA">image.NRGBA</a>.
The <a href="/pkg/image/#Image">image.Image</a> interface type has not changed,
though, and you should not need to change your code if you don't explicitly
refer to <code>Pix</code> fields. For example, if you decode a number of images
using the <a href="/pkg/image/jpeg/">image/jpeg</a> package, compose them using
<a href="/pkg/image/draw/">image/draw</a>, and then encode the result using
<a href="/pkg/img/png">image/png</a>, then your code should still work as
before.
If your code <i>does</i> refer to <code>Pix</code> fields see the
<a href="/doc/devel/weekly.html#2011-07-19">weekly.2011-07-19</a>
snapshot notes for how to update your code.
</p>
<p>
<a href="/pkg/template/">Package template</a> has been replaced with a new
templating package (formerly <code>exp/template</code>). The original template
package is still available as <a href="/pkg/old/template/">old/template</a>.
The <code>old/template</code> package is deprecated and will be removed.
The Go tree has been updated to use the new template package. We encourage
users of the old template package to switch to the new one. Code that uses
<code>template</code> or <code>exp/template</code> will need to change its
import lines to <code>"old/template"</code> or <code>"template"</code>,
respectively.
</p>
<h3 id="r60.cmd">Tools</h3>
<p>
<a href="/cmd/goinstall/">Goinstall</a> now uses a new tag selection scheme.
When downloading or updating, goinstall looks for a tag or branch with the
<code>"go."</code> prefix that corresponds to the local Go version. For Go
<code>release.r58</code> it looks for <code>go.r58</code>. For
<code>weekly.2011-06-03</code> it looks for <code>go.weekly.2011-06-03</code>.
If the specific <code>go.X</code> tag or branch is not found, it chooses the
closest earlier version. If an appropriate tag or branch is found, goinstall
uses that version of the code. Otherwise it uses the default version selected
by the version control system. Library authors are encouraged to use the
appropriate tag or branch names in their repositories to make their libraries
more accessible.
</p>
<h3 id="r60.minor">Minor revisions</h3>
<p>
r60.1 includes a
<a href="http://code.google.com/p/go/source/detail?r=1824581bf62d">linker
fix</a>, a pair of
<a href="http://code.google.com/p/go/source/detail?r=9ef4429c2c64">goplay</a>
<a href="http://code.google.com/p/go/source/detail?r=d42ed8c3098e">fixes</a>,
and a <code>json</code> package
<a href="http://code.google.com/p/go/source/detail?r=d5e97874fe84">fix</a> and
a new
<a href="http://code.google.com/p/go/source/detail?r=4f0e6269213f">struct tag
option</a>.
</p>
<p>
r60.2
<a href="http://code.google.com/p/go/source/detail?r=ff19536042ac">fixes</a>
a memory leak involving maps.
</p>
<p>
r60.3 fixes a
<a href="http://code.google.com/p/go/source/detail?r=01fa62f5e4e5">reflect bug</a>.
</p>
<h2 id="r59">r59 (released 2011/08/01)</h2>
<p>
The r59 release corresponds to
<code><a href="weekly.html#2011-07-07">weekly.2011-07-07</a></code>.
This section highlights the most significant changes in this release.
For a more detailed summary, see the
<a href="weekly.html#2011-07-07">weekly release notes</a>.
For complete information, see the
<a href="http://code.google.com/p/go/source/list?r=release-branch.r59">Mercurial change list</a>.
</p>
<h3 id="r59.lang">Language</h3>
<p>
This release includes a language change that restricts the use of
<code>goto</code>. In essence, a <code>goto</code> statement outside a block
cannot jump to a label inside that block. Your code may require changes if it
uses <code>goto</code>.
See <a href="http://code.google.com/p/go/source/detail?r=dc6d3cf9279d">this
changeset</a> for how the new rule affected the Go tree.
</p>
<h3 id="r59.pkg">Packages</h3>
<p>
As usual, <a href="/cmd/gofix/">gofix</a> will handle the bulk of the rewrites
necessary for these changes to package APIs.
</p>
<p>
<a href="/pkg/http">Package http</a> has a new
<a href="/pkg/http/#FileSystem">FileSystem</a> interface that provides access
to files. The <a href="/pkg/http/#FileServer">FileServer</a> helper now takes a
<code>FileSystem</code> argument instead of an explicit file system root. By
implementing your own <code>FileSystem</code> you can use the
<code>FileServer</code> to serve arbitrary data.
</p>
<p>
<a href="/pkg/os/">Package os</a>'s <code>ErrorString</code> type has been
hidden. Most uses of <code>os.ErrorString</code> can be replaced with
<a href="/pkg/os/#NewError">os.NewError</a>.
</p>
<p>
<a href="/pkg/reflect/">Package reflect</a> supports a new struct tag scheme
that enables sharing of struct tags between multiple packages.
In this scheme, the tags must be of the form:
</p>
<pre>
`key:"value" key2:"value2"`
</pre>
<p>
The <a href="/pkg/reflect/#StructField">StructField</a> type's Tag field now
has type <a href="/pkg/reflect/#StructTag">StructTag</a>, which has a
<code>Get</code> method. Clients of <a href="/pkg/json">json</a> and
<a href="/pkg/xml">xml</a> will need to be updated. Code that says
</p>
<pre>
type T struct {
X int "name"
}
</pre>
<p>
should become
</p>
<pre>
type T struct {
X int `json:"name"` // or `xml:"name"`
}
</pre>
<p>
Use <a href="/cmd/govet/">govet</a> to identify struct tags that need to be
changed to use the new syntax.
</p>
<p>
<a href="/pkg/sort/">Package sort</a>'s <code>IntArray</code> type has been
renamed to <a href="/pkg/sort/#IntSlice">IntSlice</a>, and similarly for
<a href="/pkg/sort/#Float64Slice">Float64Slice</a> and
<a href="/pkg/sort/#StringSlice">StringSlice</a>.
</p>
<p>
<a href="/pkg/strings/">Package strings</a>'s <code>Split</code> function has
itself been split into <a href="/pkg/strings/#Split">Split</a> and
<a href="/pkg/strings/#SplitN">SplitN</a>.
<code>SplitN</code> is the same as the old <code>Split</code>.
The new <code>Split</code> is equivalent to <code>SplitN</code> with a final
argument of -1.
</p>
<a href="/pkg/image/draw/">Package image/draw</a>'s
<a href="/pkg/image/draw/#Draw">Draw</a> function now takes an additional
argument, a compositing operator.
If in doubt, use <a href="/pkg/image/draw/#Op">draw.Over</a>.
</p>
<h3 id="r59.cmd">Tools</h3>
<p>
<a href="/cmd/goinstall/">Goinstall</a> now installs packages and commands from
arbitrary remote repositories (not just Google Code, Github, and so on).
See the <a href="/cmd/goinstall/">goinstall documentation</a> for details.
</p>
<h2 id="r58">r58 (released 2011/06/29)</h2>
<p>
The r58 release corresponds to
<code><a href="weekly.html#2011-06-09">weekly.2011-06-09</a></code>
with additional bug fixes.
This section highlights the most significant changes in this release.
For a more detailed summary, see the
<a href="weekly.html#2011-06-09">weekly release notes</a>.
For complete information, see the
<a href="http://code.google.com/p/go/source/list?r=release-branch.r58">Mercurial change list</a>.
</p>
<h3 id="r58.lang">Language</h3>
<p>
This release fixes a <a href="http://code.google.com/p/go/source/detail?r=b720749486e1">use of uninitialized memory in programs that misuse <code>goto</code></a>.
</p>
<h3 id="r58.pkg">Packages</h3>
<p>
As usual, <a href="/cmd/gofix/">gofix</a> will handle the bulk of the rewrites
necessary for these changes to package APIs.
</p>
<p>
<a href="/pkg/http/">Package http</a> drops the <code>finalURL</code> return
value from the <a href="/pkg/http/#Client.Get">Client.Get</a> method. The value
is now available via the new <code>Request</code> field on <a
href="/pkg/http/#Response">http.Response</a>.
Most instances of the type map[string][]string in have been
replaced with the new <a href="/pkg/http/#Values">Values</a> type.
</p>
<p>
<a href="/pkg/exec/">Package exec</a> has been redesigned with a more
convenient and succinct API.
</p>
<p>
<a href="/pkg/strconv/">Package strconv</a>'s <a href="/pkg/strconv/#Quote">Quote</a>
function now escapes only those Unicode code points not classified as printable
by <a href="/pkg/unicode/#IsPrint">unicode.IsPrint</a>.
Previously Quote would escape all non-ASCII characters.
This also affects the <a href="/pkg/fmt/">fmt</a> package's <code>"%q"</code>
formatting directive. The previous quoting behavior is still available via
strconv's new <a href="/pkg/strconv/#QuoteToASCII">QuoteToASCII</a> function.
</p>
<p>
<a href="/pkg/os/signal/">Package os/signal</a>'s
<a href="/pkg/os/#Signal">Signal</a> and
<a href="/pkg/os/#UnixSignal">UnixSignal</a> types have been moved to the
<a href="/pkg/os/">os</a> package.
</p>
<p>
<a href="/pkg/image/draw/">Package image/draw</a> is the new name for
<code>exp/draw</code>. The GUI-related code from <code>exp/draw</code> is now
located in the <a href="/pkg/exp/gui/">exp/gui</a> package.
</p>
<h3 id="r58.cmd">Tools</h3>
<p>
<a href="/cmd/goinstall/">Goinstall</a> now observes the GOPATH environment
variable to build and install your own code and external libraries outside of
the Go tree (and avoid writing Makefiles).
</p>
<h3 id="r58.minor">Minor revisions</h3>
<p>r58.1 adds
<a href="http://code.google.com/p/go/source/detail?r=293c25943586">build</a> and
<a href="http://code.google.com/p/go/source/detail?r=bf17e96b6582">runtime</a>
changes to make Go run on OS X 10.7 Lion.
</p>
<h2 id="r57">r57 (released 2011/05/03)</h2>
<p>
@@ -445,7 +136,7 @@ Remember that gofix will handle the bulk of the rewrites
necessary for these changes to package APIs.
</p>
<h3 id="r57.cmd">Tools</h3>
<h3 id="r57.tool">Tools</h3>
<p><a href="/cmd/gofix/">Gofix</a>, a new command, is described above.</p>

135
doc/devel/roadmap.html Normal file
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@@ -0,0 +1,135 @@
<!-- Roadmap -->
<h2 id="Roadmap">Go Roadmap</h2>
<p>
This page lists features and ideas being developed or discussed by the
Go team. This list will be updated as work continues.
<p>
The roadmap should be discussed on
the <a href="http://groups.google.com/group/golang-nuts">golang-nuts
mailing list</a>.
<h3 id="Language_roadmap">
Language roadmap</h3>
<p>
This is a list of language changes that are being considered.
Appearance on this list is no guarantee that the change will be
accepted.
<ul>
<li>
Possibly rewrite restriction on goto across variable declarations.
<li>
Variant types. A way to define a type as being the union of some set
of types.
<li>
Generics. An active topic of discussion.
<li>
Methods for operators, to allow a type to use arithmetic notation for
expressions.
<li>
Possibly allow top-level packages to be given names other than main.
</ul>
<h3 id="Implementation_roadmap">
Implementation roadmap</h3>
<ul>
<li>
Improved garbage collector.
<li>
Debugger.
<li>
App Engine support.
<li>
Improved implementation documentation.
</ul>
<h4 id="Gc_roadmap">
Gc compiler roadmap</h4>
<ul>
<li>
Implement goto restrictions.
<li>
Improved optimization.
<li>
Use escape analysis to keep more data on stack.
</ul>
<h4 id="Gccgo_roadmap">
Gccgo compiler roadmap</h4>
<ul>
<li>
Implement goto restrictions.
<li>
Use goroutines rather than threads.
<li>
Separate gcc interface from frontend proper.
<li>
Use escape analysis to keep more data on stack.
</ul>
<h4 id="Tools_roadmap">
Tools roadmap</h4>
<ul>
<li>
Strengthen goinstall until it can displace make for most builds.
</ul>
<h4 id="Packages_roadmap">
Packages roadmap</h4>
<ul>
<li>
Faster, RE2-like regular expressions.
<li>
Comprehensive support for international text.
<li>
Support for international dates, times, etc.
<li>
Support for multilingual messages.
</ul>
<h3 id="done">Done</h3>
<ul>
<li>
gc: Generate DWARF debug info.
<li>
gc: Provide gdb support for runtime facilities.
<li>
Safe compilation mode: generate code that is guaranteed not to obtain an invalid memory address other than via <code>import "unsafe"</code>.
<li>
Gccgo: garbage collection.
<li>
SWIG support.
<li>
Simpler semicolon rules.
<li>
A more general definition of <code>...</code> in parameter lists.
<li>
Explicit conversions from <code>string</code>
to <code>[]byte</code> and <code>[]int</code>.
<li>
A function that will be run by the garbage collector when an item is freed
(runtime.SetFinalizer).
<li>
Public continuous build and benchmark infrastructure (gobuilder).
<li>
Package manager (goinstall).
<li>
A means of recovering from a panic (recover).
<li>
5g: Better floating point support.
<li>
Improved CGO including some mechanism for calling back from C to Go.
<li>
Faster, allocation-light reflection.
</ul>

File diff suppressed because it is too large Load Diff

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@@ -1,176 +1,142 @@
<!--{
"Title": "Documentation",
"Path": "/doc/"
}-->
<p>
The Go programming language is an open source project to make programmers more
productive.
</p>
<p>
Go is expressive, concise, clean, and efficient. Its concurrency
mechanisms make it easy to write programs that get the most out of multicore
and networked machines, while its novel type system enables flexible and
modular program construction. Go compiles quickly to machine code yet has the
convenience of garbage collection and the power of run-time reflection. It's a
fast, statically typed, compiled language that feels like a dynamically typed,
interpreted language.
</p>
<div id="manual-nav"></div>
<h2>Installing Go</h2>
<h3><a href="/doc/install">Getting Started</a></h3>
<p>
Instructions for downloading and installing the Go compilers, tools, and
libraries.
</p>
<!-- title Documentation -->
<div class="left-column">
<h2 id="learning">Learning Go</h2>
<img class="gopher" src="/doc/gopher/doc.png"/>
<h3 id="go_tour"><a href="http://tour.golang.org/">A Tour of Go</a></h3>
<p>
An interactive introduction to Go in three sections.
The first section covers basic syntax and data structures; the second discusses
methods and interfaces; and the third introduces Go's concurrency primitives.
Each section concludes with a few exercises so you can practice what you've
learned. You can <a href="http://tour.golang.org/">take the tour online</a> or
<a href="http://code.google.com/p/go-tour/">install it locally</a>.
If you're new to Go, we recommend you work through the
<a href="go_tutorial.html">tutorial</a>. The
<a href="go_spec.html">language specification</a> has all the details should
you want to explore.
</p>
<p>
Once you've learned a little about the language,
<a href="effective_go.html">Effective Go</a> will help you learn the style and
idioms of programming in Go.
</p>
<h3 id="code"><a href="code.html">How to write Go code</a></h3>
<h3 id="orig_tutorial"><a href="go_tutorial.html">A Tutorial for the Go Programming Language</a></h3>
<p>
How to use the <a href="/cmd/go/">go command</a> to fetch, build, and install
packages, commands, and run tests.
The first tutorial. An introductory text that touches upon several core
concepts: syntax, types, allocation, constants, I/O, sorting, printing,
goroutines, and channels.
</p>
<h3 id="course_notes">Course Notes</h3>
<p>
Slides from a 3-day course about the Go programming language.
A more thorough introduction than the tutorial.
</p>
<ul>
<li><a href="GoCourseDay1.pdf">Day 1: Basics</a> <small>[270KB PDF]</small>
<li><a href="GoCourseDay2.pdf">Day 2: Types, Methods, Interfaces</a> <small>[270KB PDF]</small>
<li><a href="GoCourseDay3.pdf">Day 3: Concurrency and Communication</a> <small>[180KB PDF]</small>
</ul>
<h3 id="effective_go"><a href="effective_go.html">Effective Go</a></h3>
<p>
A document that gives tips for writing clear, idiomatic Go code.
A must read for any new Go programmer. It augments the tour and
A must read for any new Go programmer. It augments the tutorial and
the language specification, both of which should be read first.
</p>
<h3 id="appengine"><a href="http://code.google.com/appengine/docs/go/gettingstarted/">Getting Started with Go on App Engine</a></h3>
<p>
How to develop and deploy a simple Go project with
<a href="http://code.google.com/appengine/">Google App Engine</a>.
</p>
<h3 id="go_faq"><a href="go_faq.html">Frequently Asked Questions (FAQ)</a></h3>
<p>
Answers to common questions about Go.
</p>
<h3 id="wiki"><a href="http://code.google.com/p/go-wiki/wiki">Go Language Community Wiki</a></h3>
<p>A wiki maintained by the Go community.</p>
<h2 id="go1">Go version 1</h2>
<h3 id="go1notes"><a href="/doc/go1.html">Go 1 Release Notes</a></h3>
<h3 id="code"><a href="code.html">How to write Go code</a></h3>
<p>
A guide for updating your code to work with Go 1.
How to write a new package and how to test code.
</p>
<h3 id="go1compat"><a href="/doc/go1compat.html">Go 1 and the Future of Go Programs</a></h3>
<h3 id="codelab_wiki"><a href="codelab/wiki/">Codelab: Writing Web Applications</a></h3>
<p>
What Go 1 defines and the backwards-compatibility guarantees one can expect as
Go 1 matures.
This codelab takes the reader through the creation of a simple wiki web
application. It touches on structs, methods, file I/O, http, regular expressions,
and closures.
</p>
<h2 id="articles">Go Articles</h2>
<h3 id="blog"><a href="http://blog.golang.org/">The Go Blog</a></h3>
<p>The official blog of the Go project, featuring news and in-depth articles by
the Go team and guests.</p>
<h4>Codewalks</h4>
<h3 id="codewalks"><a href="codewalk/">Codewalks</a></h3>
<p>
Guided tours of Go programs.
Guided tours of Go programs.
</p>
<h3 id="go_for_cpp_programmers"><a href="go_for_cpp_programmers.html">Go for C++ Programmers</a></h3>
<p>
An introduction to Go for C++ programmers.
</p>
<h2 id="tutorials_nonenglish">Non-English Documentation</h2>
<h3 id="docs_cn">Chinese &mdash; 中文</h3>
<ul>
<li><a href="/doc/codewalk/functions">First-Class Functions in Go</a></li>
<li><a href="/doc/codewalk/markov">Generating arbitrary text: a Markov chain algorithm</a></li>
<li><a href="/doc/codewalk/sharemem">Share Memory by Communicating</a></li>
<li><a href="/doc/articles/wiki/">Writing Web Applications</a> - building a simple web application.</li>
<li><a href="http://code.google.com/p/golang-china/">golang-china</a> - a broad range of Go documentation.</li>
<li><a href="http://code.google.com/p/ac-me/downloads/detail?name=fango.pdf">Effective Go and Tutorial</a></li>
</ul>
<h4>Language</h4>
<h3 id="docs_de">German &mdash; Deutsch</h3>
<ul>
<li><a href="/doc/articles/json_rpc_tale_of_interfaces.html">JSON-RPC: a tale of interfaces</a></li>
<li><a href="/doc/articles/gos_declaration_syntax.html">Go's Declaration Syntax</a></li>
<li><a href="/doc/articles/defer_panic_recover.html">Defer, Panic, and Recover</a></li>
<li><a href="/doc/articles/concurrency_patterns.html">Go Concurrency Patterns: Timing out, moving on</a></li>
<li><a href="/doc/articles/slices_usage_and_internals.html">Go Slices: usage and internals</a></li>
<li><a href="http://blog.golang.org/2011/05/gif-decoder-exercise-in-go-interfaces.html">A GIF decoder: an exercise in Go interfaces</a></li>
<li><a href="/doc/articles/error_handling.html">Error Handling and Go</a></li>
<li><a href="http://bitloeffel.de/DOC/golang/go_tutorial_de.html">Eine Anleitung zum Programmieren in Go</a> - the Go Tutorial.</li>
<li><a href="http://bitloeffel.de/DOC/golang/effective_go_de.html">Wirkungsvoll Go programmieren</a> - Effective Go.</li>
<li><a href="http://bitloeffel.de/DOC/golang/code_de.html">Wie man Go-Kode schreibt</a> - How to Write Go Code.</li>
</ul>
<h4>Packages</h4>
<h3 id="docs_jp">Japanese &mdash; 日本語</h3>
<ul>
<li><a href="/doc/articles/json_and_go.html">JSON and Go</a> - using the <a href="/pkg/encoding/json/">json</a> package.</li>
<li><a href="/doc/articles/gobs_of_data.html">Gobs of data</a> - the design and use of the <a href="/pkg/encoding/gob/">gob</a> package.</li>
<li><a href="/doc/articles/laws_of_reflection.html">The Laws of Reflection</a> - the fundamentals of the <a href="/pkg/reflect/">reflect</a> package.</li>
<li><a href="/doc/articles/image_package.html">The Go image package</a> - the fundamentals of the <a href="/pkg/image/">image</a> package.</li>
<li><a href="/doc/articles/image_draw.html">The Go image/draw package</a> - the fundamentals of the <a href="/pkg/image/draw/">image/draw</a> package.</li>
<li><a href="http://golang.jp/">golang.jp</a> - Go documentation and news.
</ul>
<h4>Tools</h4>
<h3 id="docs_ru">Russian &mdash; Русский</h3>
<ul>
<li><a href="/doc/articles/go_command.html">About the Go command</a> - why we wrote it, what it is, what it's not, and how to use it.</li>
<li><a href="/doc/articles/c_go_cgo.html">C? Go? Cgo!</a> - linking against C code with <a href="/cmd/cgo/">cgo</a>.</li>
<li><a href="/doc/gdb">Debugging Go Code with GDB</a></li>
<li><a href="/doc/articles/godoc_documenting_go_code.html">Godoc: documenting Go code</a> - writing good documentation for <a href="/cmd/godoc/">godoc</a>.</li>
<li><a href="http://blog.golang.org/2011/06/profiling-go-programs.html">Profiling Go Programs</a></li>
<li><a href="http://golanguage.ru/">golanguage.ru</a> - Go documentation.
</ul>
<h2 id="talks">Talks</h2>
</div>
<img class="gopher" src="/doc/gopher/talks.png"/>
<div class="right-column">
<h2 id="References">References</h2>
<p>Keep these under your pillow.</p>
<h3 id="pkg"><a href="/pkg/">Package Documentation</a></h3>
<p>
The talks marked with a red asterisk (<font color="red">*</font>) were written
before Go 1 and contain some examples that are no longer correct, but they are
still of value.
The built-in documentation for the Go standard library.
</p>
<h3 id="writing_web_apps"><a href="http://www.youtube.com/watch?v=-i0hat7pdpk">Writing Web Apps in Go</a><font color="red">*</font></h3>
<h3 id="cmd"><a href="/cmd/">Command Documentation</a></h3>
<p>
A talk by Rob Pike and Andrew Gerrand presented at Google I/O 2011.
It walks through the construction and deployment of a simple web application
and unveils the <a href="http://blog.golang.org/2011/05/go-and-google-app-engine.html">Go runtime for App Engine</a>.
See the <a href="/doc/talks/io2011/Writing_Web_Apps_in_Go.pdf">presentation slides</a>.
The built-in documentation for the Go tools.
</p>
<h3 id="real_world_go"><a href="http://www.youtube.com/watch?v=7QDVRowyUQA">Real World Go</a><font color="red">*</font></h3>
<h3 id="spec"><a href="go_spec.html">Language Specification</a></h3>
<p>
A talk by Andrew Gerrand presented at Google I/O Bootcamp 2011.
It gives a broad overview of Go's type system and concurrency model
and provides four examples of Go programs that solve real problems.
See the <a href="/doc/talks/io2011/Real_World_Go.pdf">presentation slides</a>.
The official Go Language specification.
</p>
<h3 id="integrated_apps"><a href="http://www.youtube.com/watch?v=Mo1YKpIF1PQ">Building Integrated Apps on Google's Cloud Platform</a></h3>
<h3 id="go_mem"><a href="go_mem.html">The Go Memory Model</a></h3>
<p>
A talk by Andrew Gerrand presented at Google Developer Day Japan 2011.
It discusses the development of a web application that runs on Google
App Engine and renders images that it stores on Google Cloud Storage.
A document that specifies the conditions under which reads of a variable in
one goroutine can be guaranteed to observe values produced by writes to the
same variable in a different goroutine.
</p>
<h3 id="go_programming"><a href="http://www.youtube.com/watch?v=jgVhBThJdXc">Go Programming</a><font color="red">*</font></h3>
<h2 id="videos_talks">Videos and Talks</h2>
<h3 id="go_programming"><a href="http://www.youtube.com/watch?v=jgVhBThJdXc">Go Programming</a></h3>
<p>
A presentation delivered by Rob Pike and Russ Cox at Google I/O 2010. It
illustrates how programming in Go differs from other languages through a set of
examples demonstrating features particular to Go. These include concurrency,
embedded types, methods on any type, and program construction using interfaces.
embedded types, methods on any type, and program construction using interfaces.
</p>
<h3 id="practical_go_programming"><a href="http://www.youtube.com/watch?v=2-pPAvqyluI">Practical Go Programming</a><font color="red">*</font></h3>
<h3 id="practical_go_programming"><a href="http://osdc.blip.tv/file/4432146/">Practical Go Programming</a></h3>
<p>
This talk presents the development of a complete web application in Go.
It looks at design, storage, concurrency, and scaling issues in detail, using
@@ -178,37 +144,63 @@ the simple example of an URL shortening service.
See the <a href="http://wh3rd.net/practical-go/">presentation slides</a>.
</p>
<h4 id="talks_more">More</h4>
<h3 id="techtalk"><a href="http://www.youtube.com/watch?v=rKnDgT73v8s">The Go Tech Talk</a></h3>
<p>
See the <a href="http://code.google.com/p/go-wiki/wiki/GoTalks">GoTalks
page</a> at the <a href="http://code.google.com/p/go-wiki/wiki">Go Wiki</a> for
more Go talks.
An hour-long talk delivered by Rob Pike at Google in October 2009.
The language's first public introduction. (See the <a href="talks/go_talk-20091030.pdf">slides in PDF format</a>.) The language has changed since it was made,
but it's still a good introduction.
</p>
<h2 id="nonenglish">Non-English Documentation</h2>
<h3 id="gocoding_channel"><a href="http://www.youtube.com/gocoding">gocoding YouTube Channel</a></h3>
<p>
See the <a href="http://code.google.com/p/go-wiki/wiki/NonEnglish">NonEnglish</a> page
at the <a href="http://code.google.com/p/go-wiki/wiki">Go Wiki</a> for localized
documentation.
A YouTube channel that includes screencasts and other Go-related videos:
</p>
<ul>
<li><a href="http://www.youtube.com/gocoding#p/u/0/jDWBJOXs_iI">Screencast: Writing Go Packages</a> - writing, building, and distributing Go packages.</li>
<li><a href="http://www.youtube.com/watch?v=3brH0zOqm0w">Screencast: Testing Go Packages</a> - writing unit tests and benchmarking Go packages.</li>
</ul>
<h3 id="jaoo_go"><a href="/doc/ExpressivenessOfGo.pdf">The Expressiveness Of Go</a></h3>
<p>
A discussion of the qualities that make Go an expressive and comprehensible
language. The talk was presented by Rob Pike at JAOO 2010.
The recording of the event was lost due to a hardware error.
</p>
<h2 id="community">The Go Community</h2>
<h3 id="oscon_go"><a href="http://www.oscon.com/oscon2010/public/schedule/detail/14760">Another Go at Language Design</a></h3>
<p>
A tour, with some background, of the major features of Go, intended for
an audience new to the language. The talk was presented at OSCON 2010.
See the <a href="http://assets.en.oreilly.com/1/event/45/Another%20Go%20at%20Language%20Design%20Presentation.pdf">presentation slides</a>.
</p>
<p>
This talk was also delivered at Sydney University in September 2010. A video
of the lecture is available
<a href="http://sydney.edu.au/engineering/it/videos/seminar_pike">here</a>.
</p>
<img class="gopher" src="/doc/gopher/project.png"/>
<h3 id="emerging_go"><a href="http://www.oscon.com/oscon2010/public/schedule/detail/15464">Go Emerging Languages Conference Talk</a></h3>
<p>
Rob Pike's Emerging Languages Conference presentation delivered in July 2010. See the <a href="http://assets.en.oreilly.com/1/event/45/Go%20Presentation.pdf">presentation slides</a>. Abstract:
</p>
<p><i>
Gos approach to concurrency differs from that of many languages, even those
(such as Erlang) that make concurrency central, yet it has deep roots. The path
from Hoares 1978 paper to Go provides insight into how and why Go works as it
does.
</i></p>
<h3 id="mailinglist"><a href="http://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
<p>The <a href="http://groups.google.com/group/golang-nuts">golang-nuts</a>
mailing list is for general Go discussion.</p>
<h3 id="go_frontend_gcc"><a href="talks/gofrontend-gcc-summit-2010.pdf">The Go frontend for GCC</a></h3>
<p>
A description of the Go language frontend for gcc.
Ian Lance Taylor's paper delivered at the GCC Summit 2010.
</p>
<h3 id="projects"><a href="http://godashboard.appspot.com/project">Go Project Dashboard</a></h3>
<p>A list of external Go projects including programs and libraries.</p>
<h3 id="promo_video"><a href="http://www.youtube.com/watch?v=wwoWei-GAPo">The Go Promo Video</a></h3>
<p>
A short promotional video featuring Russ Cox demonstrating Go's fast compiler.
</p>
<h3 id="irc"><a href="irc:irc.freenode.net/go-nuts">Go IRC Channel</a></h3>
<p><b>#go-nuts</b> on <b>irc.freenode.net</b> is the official Go IRC channel.</p>
</div>
<h3 id="plus"><a href="https://plus.google.com/101406623878176903605/posts">The Go Programming Language at Google+</a></h3>
<p>The Go project's Google+ page.</p>
<h3 id="twitter"><a href="http://twitter.com/go_nuts">@go_nuts at Twitter</a></h3>
<p>The Go project's official Twitter account.</p>
<div class="end-columns"></div>

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@@ -1,99 +1,92 @@
<!--{
"Title": "Contributing to the gccgo frontend"
}-->
<!-- Contributing to the gccgo frontend -->
<h2>Introduction</h2>
<p>
These are some notes on contributing to the gccgo frontend for GCC.
For information on contributing to parts of Go other than gccgo,
see <a href="/doc/contribute.html">Contributing to the Go project</a>. For
information on building gccgo for yourself,
see <a href="/doc/gccgo_install.html">Setting up and using gccgo</a>.
These are some notes on contributing to the <code>gccgo</code>
frontend for GCC. For information on contributing to parts of Go other
than <code>gccgo</code>, see <a href="contribute.html">Contributing to
the Go project</a>. For information on building <code>gccgo</code>
for yourself, see <a href="gccgo_install.html">Setting up and using
gccgo</a>.
</p>
<h2>Legal Prerequisites</h2>
<p>
You must follow the <a href="/doc/contribute.html#copyright">Go copyright
rules</a> for all changes to the gccgo frontend and the associated
libgo library. Code that is part of GCC rather than gccgo must follow
the general <a href="http://gcc.gnu.org/contribute.html">GCC
contribution rules</a>.
You must follow the <a href="contribute.html#copyright">Go copyright
rules.</a>
</p>
<h2>Code</h2>
<p>
The master sources for the gccgo frontend may be found at
The source code for the <code>gccgo</code> frontend may be found at
<a href="http://code.google.com/p/gofrontend">http://code.google.com/p/gofrontend</a>.
The master sources are not buildable by themselves, but only in
conjunction with GCC (in the future, other compilers may be
supported). Changes made to the gccgo frontend are also applied to
the GCC source code repository hosted at <code>gcc.gnu.org</code>. In
the <code>gofrontend</code> repository, the <code>go</code> directory
is mirrored to the <code>gcc/go/gofrontend</code> directory in the GCC
repository, and the <code>gofrontend</code> <code>libgo</code>
directory is mirrored to the GCC <code>libgo</code> directory. In
addition, the <code>test</code> directory
from <a href="http://code.google.com/p/go">the main Go repository</a>
is mirrored to the <code>gcc/testsuite/go.test/test</code> directory
in the GCC repository.
Changes made to that project are routinely merged into the source code
hosted at <code>gcc.gnu.org</code>. The <code>gofrontend</code>
project includes only the Go frontend proper. These are the files
which in the <code>gcc</code> sources may be found in the
directories <code>gcc/go</code> and <code>libgo</code>.
The <code>gcc</code> sources also include a copy of
the <code>test</code> directory
from <a href="http://code.google.com/p/go">the main Go repository</a>.
<p>
The frontend is written in C++ and as such the GNU coding standards do
not entirely apply; in writing code for the frontend, follow the
formatting of the surrounding code. Although the frontend is
currently closely tied to the rest of the <code>gcc</code> codebase,
we plan to make it more independent. Any new code that uses other
parts of <code>gcc</code> should be placed in an appropriate file,
such as <code>gogo-tree.cc</code>. Eventually
all <code>gcc</code>-specific code should migrate to
a <code>gcc-interface</code> subdirectory.
</p>
<p>
Changes to these directories always flow from the master sources to
the GCC repository. The files should never be changed in the GCC
repository except by changing them in the master sources and mirroring
them.
</p>
<p>
The gccgo frontend is written in C++. It follows the GNU coding
standards to the extent that they apply to C++. In writing code for
the frontend, follow the formatting of the surrounding code. Although
the frontend is currently tied to the rest of the GCC codebase, we
plan to make it more independent. Eventually all GCC-specific code
will migrate out of the frontend proper and into GCC proper. In the
GCC sources this will generally mean moving code
from <code>gcc/go/gofrontend</code> to <code>gcc/go</code>.
</p>
<p>
The run-time library for gccgo is mostly the same as the library
in <a href="http://code.google.com/p/go">the main Go repository</a>.
The library code in the Go repository is periodically merged into
the <code>libgo/go</code> directory of the <code>gofrontend</code> and
then the GCC repositories, using the shell
script <code>libgo/merge.sh</code>. Accordingly, most library changes
should be made in the main Go repository. The files outside
of <code>libgo/go</code> are gccgo-specific; that said, some of the
files in <code>libgo/runtime</code> are based on files
in <code>src/pkg/runtime</code> in the main Go repository.
The run-time library for <code>gccgo</code> is mostly the same as the
library in <a href="http://code.google.com/p/go">the main Go
repository</a>. The library code in the Go repository is periodically
copied into the <code>gofrontend</code> and the <code>gcc</code>
repositories. Accordingly, most library changes should be made in the
main Go repository. Changes to the few <code>gccgo</code>-specific
parts of the library should follow the process described here.
The <code>gccgo</code>-specific parts of the library are everything in
the <code>libgo</code> directory except for the <code>libgo/go</code>
subdirectory.
</p>
<h2>Testing</h2>
<p>
All patches must be tested. A patch that introduces new failures is
not acceptable.
All patches must be tested. There are two test suites. A patch that
introduces new failures is not acceptable.
</p>
<p>
To run the gccgo test suite, run <code>make check-go</code> in your
build directory. This will run various tests
under <code>gcc/testsuite/go.*</code> and will also run
the <code>libgo</code> testsuite. This copy of the tests from the
main Go repository is run using the DejaGNU script found in
in <code>gcc/testsuite/go.test/go-test.exp</code>.
To run the compiler test suite, run <code>make check-go</code> in the
<code>gcc</code> subdirectory of your build directory. This will run
various tests underneath <code>gcc/testsuite/go.*</code>. This
includes a copy of the tests in the main Go repository, which are run
using the DejaGNU script found in
in <code>gcc/testsuite/go.test/go-test.exp</code>. Many of the
compiler tests may be run without the Go library, but some do require
the library to built first.
</p>
<p>
Most new tests should be submitted to the main Go repository for later
mirroring into the GCC repository. If there is a need for specific
tests for gccgo, they should go in
To run the library test suite, run <code>make
check-target-libgo</code> in the top level of your build directory.
</p>
<p>
Most new tests should be submitted to the main Go repository for
copying into the <code>gccgo</code> repository. If there is a need
for specific tests for <code>gccgo</code>, they should go in
the <code>gcc/testsuite/go.go-torture</code>
or <code>gcc/testsuite/go.dg</code> directories in the GCC repository.
or <code>gcc/testsuite/go.dg</code> directories in
the <code>gcc.gnu.org</code> repository.
</p>
<h2>Submitting Changes</h2>
@@ -102,5 +95,5 @@ or <code>gcc/testsuite/go.dg</code> directories in the GCC repository.
Changes to the Go frontend should follow the same process as for the
main Go repository, only for the <code>gofrontend</code> project
rather than the <code>go</code> project. Those changes will then be
merged into the GCC sources.
merged into the <code>gcc</code> sources.
</p>

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@@ -1,63 +1,37 @@
<!--{
"Title": "Setting up and using gccgo",
"Path": "/doc/install/gccgo"
}-->
<!-- Setting up and using gccgo -->
<p>
This document explains how to use gccgo, a compiler for
the Go language. The gccgo compiler is a new frontend
for GCC, the widely used GNU compiler. Although the
frontend itself is under a BSD-style license, gccgo is
normally used as part of GCC and is then covered by
This document explains how to use <code>gccgo</code>, a compiler for
the Go language. The <code>gccgo</code> compiler is a new frontend
for <code>gcc</code>, the widely used GNU compiler. Although the
frontend itself is under a BSD-style license, <code>gccgo</code> is
normally used as part of <code>gcc</code> and is then covered by
the <a href="http://www.gnu.org/licenses/gpl.html">GNU General Public
License</a> (the license covers gccgo itself as part of GCC; it
does not cover code generated by gccgo).
License</a>.
</p>
<p>
Note that gccgo is not the <code>gc</code> compiler; see
the <a href="/doc/install.html">Installing Go</a> instructions for that
Note that <code>gccgo</code> is not the <code>6g</code> compiler; see
the <a href="install.html">Installing Go</a> instructions for that
compiler.
</p>
<h2 id="Releases">Releases</h2>
<p>
The simplest way to install gccgo is to install a GCC binary release
built to include Go support. GCC binary releases are available from
<a href="http://gcc.gnu.org/install/binaries.html">various
websites</a> and are typically included as part of GNU/Linux
distributions. We expect that most people who build these binaries
will include Go support.
</p>
<p>
The GCC 4.7.0 release includes Go support that is very close to
<a href="/doc/go1.html">Go 1</a>. Due to release timing it will not
include the last few changes to the Go 1 libraries. The GCC 4.7.1
release should include a complete Go 1 compiler and libraries.
</p>
<h2 id="Source_code">Source code</h2>
<p>
If you cannot use a release, or prefer to build gccgo for
yourself,
the gccgo source code is accessible via Subversion. The
GCC web site
The <code>gccgo</code> source code is accessible via Subversion. The
<code>gcc</code> web site
has <a href="http://gcc.gnu.org/svn.html">instructions for getting the
GCC source code</a>. The gccgo source code is included. As a
convenience, a stable version of the Go support is available in
a branch of the main GCC code
<code>gcc</code> source code</a>. The <code>gccgo</code> source code
is a branch of the main <code>gcc</code> code
repository: <code>svn://gcc.gnu.org/svn/gcc/branches/gccgo</code>.
This branch is periodically updated with stable Go compiler sources.
</p>
<p>
Note that although <code>gcc.gnu.org</code> is the most convenient way
to get the source code for the Go frontend, it is not where the master
sources live. If you want to contribute changes to the Go frontend
compiler, see <a href="/doc/gccgo_contribute.html">Contributing to
to get the source code for the compiler, that is not where the master
sources live. If you want to contribute changes to the gccgo
compiler, see <a href="gccgo_contribute.html">Contributing to
gccgo</a>.
</p>
@@ -65,37 +39,29 @@ gccgo</a>.
<h2 id="Building">Building</h2>
<p>
Building gccgo is just like building GCC
Building <code>gccgo</code> is just like building <code>gcc</code>
with one or two additional options. See
the <a href="http://gcc.gnu.org/install/">instructions on the gcc web
site</a>. When you run <code>configure</code>, add the
option <code>--enable-languages=c,c++,go</code> (along with other
languages you may want to build). If you are targeting a 32-bit x86,
then you will want to build gccgo to default to
then you will want to build <code>gccgo</code> to default to
supporting locked compare and exchange instructions; do this by also
using the <code>configure</code> option <code>--with-arch=i586</code>
(or a newer architecture, depending on where you need your programs to
run). If you are targeting a 64-bit x86, but sometimes want to use
the <code>-m32</code> option, then use the <code>configure</code>
option <code>--with-arch-32=i586</code>.
run).
</p>
<h3 id="Gold">Gold</h3>
<p>
On x86 GNU/Linux systems the gccgo compiler is able to
On x86 GNU/Linux systems the <code>gccgo</code> compiler is able to
use a small discontiguous stack for goroutines. This permits programs
to run many more goroutines, since each goroutine can use a relatively
small stack. Doing this requires using the gold linker version 2.22
or later. You can either install GNU binutils 2.22 or later, or you
can build gold yourself.
</p>
<p>
To build gold yourself, build the GNU binutils,
using <code>--enable-gold=default</code> when you run
the <code>configure</code> script. Before building, you must install
the flex and bison packages. A typical sequence would look like
small stack. Doing this requires using a development version of
the <code>gold</code> linker. The easiest way to do this is to build
the GNU binutils, using <code>--enable-gold</code> when you run
the <code>configure</code> script, and to
use <code>--with-ld=GOLD_BINARY</code> when you
configure <code>gccgo</code>. A typical sequence would look like
this (you can replace <code>/opt/gold</code> with any directory to
which you have write access):
</p>
@@ -103,79 +69,38 @@ which you have write access):
<pre>
cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
[password is "anoncvs"]
[The next command will create a directory named src, not binutils]
cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
mkdir binutils-objdir
cd binutils-objdir
../src/configure --enable-gold=default --prefix=/opt/gold
../src/configure --enable-gold --prefix=/opt/gold
make
make install
</pre>
<p>
However you install gold, when you configure gccgo, use the
option <code>--with-ld=<var>GOLD_BINARY</var></code>.
</p>
<h3 id="Prerequisites">Prerequisites</h3>
<p>
A number of prerequisites are required to build GCC, as
described on
the <a href="http://gcc.gnu.org/install/prerequisites.html">gcc web
site</a>. It is important to install all the prerequisites before
running the gcc <code>configure</code> script.
<h3 id="Build_commands">Build commands</h3>
<p>
Once all the prerequisites are installed, then a typical build and
install sequence would look like this (only use
the <code>--with-ld</code> option if you are using the gold linker as
described above):
A number of prerequisites are required to build <code>gcc</code>, as
described on the <a href="http://gcc.gnu.org/">gcc web site</a>. If
those are all available, then a typical build and install sequence
would look like this (only use the <code>--with-ld</code> option if
you built and installed the gold linker as described above):
</p>
<pre>
svn checkout svn://gcc.gnu.org/svn/gcc/branches/gccgo gccgo
mkdir objdir
cd objdir
../gccgo/configure --prefix=/opt/gccgo --enable-languages=c,c++,go --with-ld=/opt/gold/bin/ld
../gccgo/configure --enable-languages=c,c++,go --with-ld=/opt/gold/bin/ld
make
make install
</pre>
<h3 id="Ubuntu">A note on Ubuntu</h3>
<p>
Current versions of Ubuntu and current versions of gcc disagree on
where system libraries and header files are found. This is not a
gccgo issue, and we hope this will be resolved soon. Until it is,
setting these environment variables while configuring and building
gccgo may fix the problem.
</p>
<pre>
LIBRARY_PATH=/usr/lib/x86_64-linux-gnu
C_INCLUDE_PATH=/usr/include/x86_64-linux-gnu
CPLUS_INCLUDE_PATH=/usr/include/x86_64-linux-gnu
export LIBRARY_PATH C_INCLUDE_PATH CPLUS_INCLUDE_PATH
</pre>
<h2 id="Using_gccgo">Using gccgo</h2>
<p>
The gccgo compiler works like other gcc frontends. The gccgo
installation does not currently include a version of
the <code>go</code> command. However if you have the <code>go</code>
command from an installation of the <code>gc</code> compiler, you can
use it with gccgo by passing the option <code>-compiler gccgo</code>
to <code>go build</code> or <code>go install</code> or <code>go
test</code>.
</p>
The <code>gccgo</code> compiler works like other gcc frontends.
<p>
To compile a file without using the <code>go</code> command:
</p>
To compile a file:
<pre>
gccgo -c file.go
@@ -184,7 +109,6 @@ gccgo -c file.go
<p>
That produces <code>file.o</code>. To link files together to form an
executable:
</p>
<pre>
gccgo -o file file.o
@@ -192,68 +116,44 @@ gccgo -o file file.o
<p>
To run the resulting file, you will need to tell the program where to
find the compiled Go packages. There are a few ways to do this:
</p>
<ul>
<li>
<p>
Set the <code>LD_LIBRARY_PATH</code> environment variable:
</p>
find the compiled Go packages. This can be done either by setting
<code>LD_LIBRARY_PATH</code> in your environment:
<pre>
LD_LIBRARY_PATH=${prefix}/lib/gcc/MACHINE/VERSION
[or]
LD_LIBRARY_PATH=${prefix}/lib64/gcc/MACHINE/VERSION
export LD_LIBRARY_PATH
LD_LIBRARY_PATH=/usr/lib/gcc/MACHINE/VERSION
</pre>
<p>
Here <code>${prefix}</code> is the <code>--prefix</code> option used
when building gccgo. For a binary install this is
normally <code>/usr</code>. Whether to use <code>lib</code>
or <code>lib64</code> depends on the target.
Typically <code>lib64</code> is correct for x86_64 systems,
and <code>lib</code> is correct for other systems. The idea is to
name the directory where <code>libgo.so</code> is found.
</p>
</li>
<li>
<p>
Passing a <code>-Wl,-R</code> option when you link:
</p>
or by passing a <code>-Wl,-R</code> option when you link:
<pre>
gccgo -o file file.o -Wl,-R,${prefix}/lib/gcc/MACHINE/VERSION
[or]
gccgo -o file file.o -Wl,-R,${prefix}/lib64/gcc/MACHINE/VERSION
gccgo -o file file.o -Wl,-R,/usr/lib/gcc/MACHINE/VERSION
</pre>
</li>
<li>
<p>
Use the <code>-static-libgo</code> option to link statically against
the compiled packages.
</p>
</li>
or you can use the <code>-static-libgo</code> link-time option to link
statically against libgo, or you can do a fully static link (static
linking is the default for the <code>6l</code> Go linker). On most
systems, a static link will look something like:
<pre>
gccgo -o file file.o -static -L /usr/lib/nptl -lgobegin -lgo -lpthread
</pre>
<li>
<p>
Use the <code>-static</code> option to do a fully static link (the
default for the <code>gc</code> compiler).
</p>
</li>
</ul>
You may get a warning about not creating an <code>.eh_frame_hdr</code>
section; this has nothing to do with Go, and may be ignored. In the
future the requirement of explicitly specifying
<code>-L /usr/lib/nptl -lgobegin -lgo -lpthread</code>
may be removed.
<h2 id="Options">Options</h2>
<p>
The gccgo compiler supports all GCC options
The <code>gccgo</code> compiler supports all <code>gcc</code> options
that are language independent, notably the <code>-O</code>
and <code>-g</code> options.
</p>
<p>
The <code>-fgo-prefix=PREFIX</code> option may be used to set a unique
@@ -262,24 +162,28 @@ use with large programs that contain many packages, in order to allow
multiple packages to use the same identifier as the package name.
The <code>PREFIX</code> may be any string; a good choice for the
string is the directory where the package will be installed.
</p>
<p>
The <code>-fno-require-return-statement</code> option may be used to
disable the compiler error about functions missing return statements.
Note that there is no way to disable this error in <code>6g</code>.
<p>
The <code>-I</code> and <code>-L</code> options, which are synonyms
for the compiler, may be used to set the search path for finding
imports.
</p>
<h2 id="Imports">Imports</h2>
<p>
When you compile a file that exports something, the export
information will be stored directly in the object file. When
you import a package, you must tell gccgo how to
When you compile a file which exports something, the export
information will be stored directly in the object file. When
you import a package, you must tell <code>gccgo</code> how to
find the file.
<p>
When you import the package <var>FILE</var> with gccgo,
When you import the package <var>FILE</var> with <code>gccgo</code>,
it will look for the import data in the following files, and use the
first one that it finds.
@@ -294,25 +198,21 @@ first one that it finds.
<code><var>FILE</var>.gox</code>, when used, will typically contain
nothing but export data. This can be generated from
<code><var>FILE</var>.o</code> via
</p>
<pre>
objcopy -j .go_export FILE.o FILE.gox
</pre>
<p>
The gccgo compiler will look in the current
directory for import files. In more complex scenarios you
The <code>gccgo</code> compiler will look in the current
directory for import files. In more complex scenarios you
may pass the <code>-I</code> or <code>-L</code> option to
gccgo. Both options take directories to search. The
<code>gccgo</code>. Both options take directories to search. The
<code>-L</code> option is also passed to the linker.
</p>
<p>
The gccgo compiler does not currently (2012-03-20) record
The <code>gccgo</code> compiler does not currently (2009-11-06) record
the file name of imported packages in the object file. You must
arrange for the imported data to be linked into the program.
</p>
<pre>
gccgo -c mypackage.go # Exports mypackage
@@ -320,41 +220,48 @@ gccgo -c main.go # Imports mypackage
gccgo -o main main.o mypackage.o # Explicitly links with mypackage.o
</pre>
<h2 id="Unimplemented">Unimplemented</h2>
<p>
Some Go features are not yet implemented in <code>gccgo</code>. As of
2010-08-23, the following are not implemented:
<ul>
<li>goroutines are implemented as NPTL threads. If you can not use
the gold linker as described above, they are created with a fixed
stack size, and the number of goroutines that may be created at
one time is limited.
</ul>
<h2 id="Debugging">Debugging</h2>
<p>
If you use the <code>-g</code> option when you compile, you can run
<code>gdb</code> on your executable. The debugger has only limited
knowledge about Go. You can set breakpoints, single-step,
<code>gdb</code> on your executable. The debugger doesn't (yet)
know anything about Go. However, you can set breakpoints, single-step,
etc. You can print variables, but they will be printed as though they
had C/C++ types. For numeric types this doesn't matter. Go strings
and interfaces will show up as two-element structures. Go
maps and channels are always represented as C pointers to run-time
structures.
</p>
had C/C++ types. For numeric types this doesn't matter. Go strings
will show up as pointers to structures; to see the value
<code>print *stringvar</code>. In general Go strings, maps, channels
and interfaces are always represented as C pointers.
<h2 id="C_Interoperability">C Interoperability</h2>
<p>
When using gccgo there is limited interoperability with C,
When using <code>gccgo</code> there is limited interoperability with C,
or with C++ code compiled using <code>extern "C"</code>.
</p>
<h3 id="Types">Types</h3>
<p>
Basic types map directly: an <code>int</code> in Go is an <code>int</code>
in C, an <code>int32</code> is an <code>int32_t</code>,
etc. Go <code>byte</code> is equivalent to C <code>unsigned
char</code>.
in C, etc. Go <code>byte</code> is equivalent to C <code>unsigned char</code>.
Pointers in Go are pointers in C. A Go <code>struct</code> is the same as C
<code>struct</code> with the same fields and types.
</p>
<p>
The Go <code>string</code> type is currently defined as a two-element
structure (this is <b style="color: red;">subject to change</b>):
</p>
<pre>
struct __go_string {
@@ -369,12 +276,10 @@ array in Go is equivalent to a C pointer to the
equivalent of the element type.
For example, Go <code>*[10]int</code> is equivalent to C <code>int*</code>,
assuming that the C pointer does point to 10 elements.
</p>
<p>
A slice in Go is a structure. The current definition is
(this is <b style="color: red;">subject to change</b>):
</p>
<pre>
struct __go_slice {
@@ -386,10 +291,9 @@ struct __go_slice {
<p>
The type of a Go function with no receiver is equivalent to a C function
whose parameter types are equivalent. When a Go function returns more
than one value, the C function returns a struct. For example, these
whose parameter types are equivalent. When a Go function returns more
than one value, the C function returns a struct. For example, these
functions have equivalent types:
</p>
<pre>
func GoFunction(int) (int, float64)
@@ -398,9 +302,7 @@ struct { int i; float64 f; } CFunction(int)
<p>
A pointer to a Go function is equivalent to a pointer to a C function
when the functions have equivalent types (this is
<b style="color: red;">subject to change</b>).
</p>
when the functions have equivalent types.
<p>
Go <code>interface</code>, <code>channel</code>, and <code>map</code>
@@ -412,7 +314,6 @@ which one is difficult to predict in general; use a cast. C <code>union</code>
types have no corresponding Go type. C <code>struct</code> types containing
bitfields have no corresponding Go type. C++ <code>class</code> types have
no corresponding Go type.
</p>
<p>
Memory allocation is completely different between C and Go, as Go uses
@@ -424,48 +325,43 @@ while the Go side still has a copy the program will fail. When passing a
pointer from Go to C, the Go function must retain a visible copy of it in
some Go variable. Otherwise the Go garbage collector may delete the
pointer while the C function is still using it.
</p>
<h3 id="Function_names">Function names</h3>
<p>
Go code can call C functions directly using a Go extension implemented
in gccgo: a function declaration may be preceded by
<code>//extern NAME</code>. For example, here is how the C function
in <code>gccgo</code>: a function declaration may be followed by
<code>__asm__("NAME")</code>. For example, here is how the C function
<code>open</code> can be declared in Go:
</p>
<pre>
//extern open
func c_open(name *byte, mode int, perm int) int
func c_open(name *byte, mode int, perm int) int __asm__ ("open");
</pre>
<p>
The C function naturally expects a NUL-terminated string, which in
The C function naturally expects a nul terminated string, which in
Go is equivalent to a pointer to an array (not a slice!) of
<code>byte</code> with a terminating zero byte. So a sample call
from Go would look like (after importing the <code>syscall</code> package):
</p>
from Go would look like (after importing the <code>os</code> package):
<pre>
var name = [4]byte{'f', 'o', 'o', 0};
i := c_open(&amp;name[0], syscall.O_RDONLY, 0);
i := c_open(&amp;name[0], os.O_RDONLY, 0);
</pre>
<p>
(this serves as an example only, to open a file in Go please use Go's
<code>os.Open</code> function instead).
</p>
<p>
The name of Go functions accessed from C is subject to change. At present
the name of a Go function that does not have a receiver is
<code>prefix.package.Functionname</code>. The prefix is set by
the <code>-fgo-prefix</code> option used when the package is compiled;
if the option is not used, the default is <code>go</code>.
if the option is not used, the default is simply <code>go</code>.
To call the function from C you must set the name using
a GCC extension.
</p>
a <code>gcc</code> extension similar to the <code>gccgo</code>
extension.
<pre>
extern int go_function(int) __asm__ ("myprefix.mypackage.Function");
@@ -475,35 +371,37 @@ extern int go_function(int) __asm__ ("myprefix.mypackage.Function");
Automatic generation of Go declarations from C source code</h3>
<p>
The Go version of GCC supports automatically generating
Go declarations from C code. The facility is rather awkward, and most
users should use the <a href="/cmd/cgo">cgo</a> program with
the <code>-gccgo</code> option instead.
</p>
The Go version of <code>gcc</code> supports automatically generating
Go declarations from C code. The facility is rather awkward at present,
and a better mechanism is under development.
<p>
Compile your C code as usual, and add the option
<code>-fdump-go-spec=<var>FILENAME</var></code>. This will create the
file <code><var>FILENAME</var></code> as a side effect of the
compilation. This file will contain Go declarations for the types,
variables and functions declared in the C code. C types that can not
be represented in Go will be recorded as comments in the Go code. The
generated file will not have a <code>package</code> declaration, but
can otherwise be compiled directly by gccgo.
</p>
Compile your C code as usual, but replace <code>-c</code> with
<code>-S&nbsp;-ggo</code>. The result will be an assembler file
with a <code>.s</code> extension. This assembler file will contain
comments beginning with #GO. Those comments are declarations in the Go
language for the C types, variables and functions declared in the C code.
C types which can not be represented in Go will contain the string INVALID.
Unsupported macro definitions will be recorded as <code>unknowndefine</code>,
and uses of <code>#undef</code> will be recorded as <code>undef</code>.
So it is very approximately possible to get Go code by running
<pre>
gcc -S -ggo foo.c
grep '#GO' foo.s | grep -v INVALID | grep -v unknowndefine | grep -v undef > foo.go
</pre>
<p>
This procedure is full of unstated caveats and restrictions and we make no
guarantee that it will not change in the future. It is more useful as a
starting point for real Go code than as a regular procedure.
</p>
<h2 id="RTEMS_Port">RTEMS Port</h2>
<p>
The gccgo compiler has been ported to <a href="http://www.rtems.com/">
The <code>gccgo</code> compiler has been ported to <a href="http://www.rtems.com/">
<code>RTEMS</code></a>. <code>RTEMS</code> is a real-time executive
that provides a high performance environment for embedded applications
on a range of processors and embedded hardware. The current gccgo
on a range of processors and embedded hardware. The current <code>gccgo</code>
port is for x86. The goal is to extend the port to most of the
<a href="http://www.rtems.org/wiki/index.php/SupportedCPUs">
architectures supported by <code>RTEMS</code></a>. For more information on the port,

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@@ -1,166 +0,0 @@
<!--{
"Title": "Go 1 and the Future of Go Programs"
}-->
<h2 id="introduction">Introduction</h2>
<p>
The release of Go version 1, Go 1 for short, is a major milestone
in the development of the language. Go 1 is a stable platform for
the growth of programs and projects written in Go.
</p>
<p>
Go 1 defines two things: first, the specification of the language;
and second, the specification of a set of core APIs, the "standard
packages" of the Go library. The Go 1 release includes their
implementation in the form of two compiler suites (gc and gccgo),
and the core libraries themselves.
</p>
<p>
It is intended that programs written to the Go 1 specification will
continue to compile and run correctly, unchanged, over the lifetime
of that specification. At some indefinite point, a Go 2 specification
may arise, but until that time, Go programs that work today should
continue to work even as future "point" releases of Go 1 arise (Go
1.1, Go 1.2, etc.).
</p>
<p>
Compatibility is at the source level. Binary compatibility for
compiled packages is not guaranteed between releases. After a point
release, Go source will need to be recompiled to link against the
new release.
</p>
<p>
The APIs may grow, acquiring new packages and features, but not in
a way that breaks existing Go 1 code.
</p>
<h2 id="expectations">Expectations</h2>
<p>
Although we expect that the vast majority of programs will maintain
this compatibility over time, it is impossible to guarantee that
no future change will break any program. This document is an attempt
to set expectations for the compatibility of Go 1 software in the
future. There are a number of ways in which a program that compiles
and runs today may fail to do so after a future point release. They
are all unlikely but worth recording.
</p>
<ul>
<li>
Security. A security issue in the specification or implementation
may come to light whose resolution requires breaking compatibility.
We reserve the right to address such security issues.
</li>
<li>
Unspecified behavior. The Go specification tries to be explicit
about most properties of the language, but there are some aspects
that are undefined. Programs that depend on such unspecified behavior
may break in future releases.
</li>
<li>
Specification errors. If it becomes necessary to address an
inconsistency or incompleteness in the specification, resolving the
issue could affect the meaning or legality of existing programs.
We reserve the right to address such issues, including updating the
implementations. Except for security issues, no incompatible changes
to the specification would be made.
</li>
<li>
Bugs. If a compiler or library has a bug that violates the
specification, a program that depends on the buggy behavior may
break if the bug is fixed. We reserve the right to fix such bugs.
</li>
<li>
Struct literals. For the addition of features in later point
releases, it may be necessary to add fields to exported structs in
the API. Code that uses untagged struct literals (such as pkg.T{3,
"x"}) to create values of these types would fail to compile after
such a change. However, code that uses tagged literals (pkg.T{A:
3, B: "x"}) will continue to compile after such a change. We will
update such data structures in a way that allows tagged struct
literals to remain compatible, although untagged literals may fail
to compile. (There are also more intricate cases involving nested
data structures or interfaces, but they have the same resolution.)
We therefore recommend that composite literals whose type is defined
in a separate package should use the tagged notation.
</li>
<li>
Dot imports. If a program imports a standard package
using <code>import . "path"</code>, additional names defined in the
imported package in future releases may conflict with other names
defined in the program. We do not recommend the use of <code>import .</code>
outside of tests, and using it may cause a program to fail
to compile in future releases.
</li>
</ul>
<p>
Of course, for all of these possibilities, should they arise, we
would endeavor whenever feasible to update the specification,
compilers, or libraries without affecting existing code.
</p>
<p>
These same considerations apply to successive point releases. For
instance, code that runs under Go 1.2 should be compatible with Go
1.2.1, Go 1.3, Go 1.4, etc., although not necessarily with Go 1.1
since it may use features added only in Go 1.2
</p>
<p>
Features added between releases, available in the source repository
but not part of the numbered binary releases, are under active
development. No promise of compatibility is made for software using
such features until they have been released.
</p>
<p>
Finally, although it is not a correctness issue, it is possible
that the performance of a program may be affected by
changes in the implementation of the compilers or libraries upon
which it depends.
No guarantee can be made about the performance of a
given program between releases.
</p>
<p>
Although these expectations apply to Go 1 itself, we hope similar
considerations would be made for the development of externally
developed software based on Go 1.
</p>
<h2 id="subrepos">Sub-repositories</h2>
<p>
Code in sub-repositories of the main go tree, such as
<a href="http://code.google.com/p/go.net">code.google.com/p/go.net</a>,
may be developed under
looser compatibility requirements. However, the sub-repositories
will be tagged as appropriate to identify versions that are compatible
with the Go 1 point releases.
</p>
<h2 id="tools">Tools</h2>
<p>
Finally, the Go tool chain (compilers, linkers, build tools, and so
on) are under active development and may change behavior. This
means, for instance, that scripts that depend on the location and
properties of the tools may be broken by a point release.
</p>
<p>
These caveats aside, we believe that Go 1 will be a firm foundation
for the development of Go and its ecosystem.
</p>

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@@ -0,0 +1,707 @@
<!-- Go For C++ Programmers -->
<p>
Go is a systems programming language intended to be a general-purpose
systems language, like C++.
These are some notes on Go for experienced C++ programmers. This
document discusses the differences between Go and C++, and says little
to nothing about the similarities.
<p>
For a more general introduction to Go, see the
<a href="go_tutorial.html">Go tutorial</a> and
<a href="effective_go.html">Effective Go</a>.
<p>
For a detailed description of the Go language, see the
<a href="go_spec.html">Go spec</a>.
<h2 id="Conceptual_Differences">Conceptual Differences</h2>
<ul>
<li>Go does not have classes with constructors or destructors.
Instead of class methods, a class inheritance hierarchy,
and virtual functions, Go provides <em>interfaces</em>, which are
<a href="#Interfaces">discussed in more detail below</a>.
Interfaces are also used where C++ uses templates.
<li>Go uses garbage collection. It is not necessary (or possible)
to release memory explicitly. The garbage collection is (intended to be)
incremental and highly efficient on modern processors.
<li>Go has pointers but not pointer arithmetic. You cannot
use a pointer variable to walk through the bytes of a string.
<li>Arrays in Go are first class values. When an array is used as a
function parameter, the function receives a copy of the array, not
a pointer to it. However, in practice functions often use slices
for parameters; slices hold pointers to underlying arrays. Slices
are <a href="#Slices">discussed further below</a>.
<li>Strings are provided by the language. They may not be changed once they
have been created.
<li>Hash tables are provided by the language. They are called maps.
<li>Separate threads of execution, and communication channels between
them, are provided by the language. This
is <a href="#Goroutines">discussed further below</a>.
<li>Certain types (maps and channels, described further below)
are passed by reference, not by value. That is, passing a map to a
function does not copy the map, and if the function changes the map
the change will be seen by the caller. In C++ terms, one can
think of these as being reference types.
<li>Go does not use header files. Instead, each source file is part of a
defined <em>package</em>. When a package defines an object
(type, constant, variable, function) with a name starting with an
upper case letter, that object is visible to any other file which
imports that package.
<li>Go does not support implicit type conversion. Operations that mix
different types require casts (called conversions in Go).
<li>Go does not support function overloading and does not support user
defined operators.
<li>Go does not support <code>const</code> or <code>volatile</code> qualifiers.
<li>Go uses <code>nil</code> for invalid pointers, where C++ uses
<code>NULL</code> or simply <code>0</code>.
</ul>
<h2 id="Syntax">Syntax</h2>
<p>
The declaration syntax is reversed compared to C++. You write the name
followed by the type. Unlike in C++, the syntax for a type does not match
the way in which the variable is used. Type declarations may be read
easily from left to right.
<pre>
<b>Go C++</b>
var v1 int // int v1;
var v2 string // const std::string v2; (approximately)
var v3 [10]int // int v3[10];
var v4 []int // int* v4; (approximately)
var v5 struct { f int } // struct { int f; } v5;
var v6 *int // int* v6; (but no pointer arithmetic)
var v7 map[string]int // unordered_map&lt;string, int&gt;* v7; (approximately)
var v8 func(a int) int // int (*v8)(int a);
</pre>
<p>
Declarations generally take the form of a keyword followed by the name
of the object being declared. The keyword is one of <code>var</code>,
<code>func</code>,
<code>const</code>, or <code>type</code>. Method declarations are a minor
exception in that
the receiver appears before the name of the object being declared; see
the <a href="#Interfaces">discussion of interfaces</a>.
<p>
You can also use a keyword followed by a series of declarations in
parentheses.
<pre>
var (
i int
m float64
)
</pre>
<p>
When declaring a function, you must either provide a name for each parameter
or not provide a name for any parameter; you can't omit some names
and provide others. You may group several names with the same type:
<pre>
func f(i, j, k int, s, t string)
</pre>
<p>
A variable may be initialized when it is declared. When this is done,
specifying the type is permitted but not required. When the type is
not specified, the type of the variable is the type of the
initialization expression.
<pre>
var v = *p
</pre>
<p>
See also the <a href="#Constants">discussion of constants, below</a>.
If a variable is not initialized explicitly, the type must be specified.
In that case it will be
implicitly initialized to the type's zero value (0, nil, etc.). There are no
uninitialized variables in Go.
<p>
Within a function, a short declaration syntax is available with
<code>:=</code> .
<pre>
v1 := v2
</pre>
<p>
This is equivalent to
<pre>
var v1 = v2
</pre>
<p>
Go permits multiple assignments, which are done in parallel.
<pre>
i, j = j, i // Swap i and j.
</pre>
<p>
Functions may have multiple return values, indicated by a list in
parentheses. The returned values can be stored by assignment
to a list of variables.
<pre>
func f() (i int, j int) { ... }
v1, v2 = f()
</pre>
<p>
Go code uses very few semicolons in practice. Technically, all Go
statements are terminated by a semicolon. However, Go treats the end
of a non-blank line as a semicolon unless the line is clearly
incomplete (the exact rules are
in <a href="go_spec.html#Semicolons">the language specification</a>).
A consequence of this is that in some cases Go does not permit you to
use a line break. For example, you may not write
<pre>
func g()
{ // INVALID
}
</pre>
A semicolon will be inserted after <code>g()</code>, causing it to be
a function declaration rather than a function definition. Similarly,
you may not write
<pre>
if x {
}
else { // INVALID
}
</pre>
A semicolon will be inserted after the <code>}</code> preceding
the <code>else</code>, causing a syntax error.
<p>
Since semicolons do end statements, you may continue using them as in
C++. However, that is not the recommended style. Idiomatic Go code
omits unnecessary semicolons, which in practice is all of them other
than the initial <code>for</code> loop clause and cases where you want several
short statements on a single line.
<p>
While we're on the topic, we recommend that rather than worry about
semicolons and brace placement, you format your code with
the <code>gofmt</code> program. That will produce a single standard
Go style, and let you worry about your code rather than your
formatting. While the style may initially seem odd, it is as good as
any other style, and familiarity will lead to comfort.
<p>
When using a pointer to a struct, you use <code>.</code> instead
of <code>-&gt;</code>.
Thus syntactically speaking a structure and a pointer to a structure
are used in the same way.
<pre>
type myStruct struct { i int }
var v9 myStruct // v9 has structure type
var p9 *myStruct // p9 is a pointer to a structure
f(v9.i, p9.i)
</pre>
<p>
Go does not require parentheses around the condition of a <code>if</code>
statement, or the expressions of a <code>for</code> statement, or the value of a
<code>switch</code> statement. On the other hand, it does require curly braces
around the body of an <code>if</code> or <code>for</code> statement.
<pre>
if a &lt; b { f() } // Valid
if (a &lt; b) { f() } // Valid (condition is a parenthesized expression)
if (a &lt; b) f() // INVALID
for i = 0; i &lt; 10; i++ {} // Valid
for (i = 0; i &lt; 10; i++) {} // INVALID
</pre>
<p>
Go does not have a <code>while</code> statement nor does it have a
<code>do/while</code>
statement. The <code>for</code> statement may be used with a single condition,
which makes it equivalent to a <code>while</code> statement. Omitting the
condition entirely is an endless loop.
<p>
Go permits <code>break</code> and <code>continue</code> to specify a label.
The label must
refer to a <code>for</code>, <code>switch</code>, or <code>select</code>
statement.
<p>
In a <code>switch</code> statement, <code>case</code> labels do not fall
through. You can
make them fall through using the <code>fallthrough</code> keyword. This applies
even to adjacent cases.
<pre>
switch i {
case 0: // empty case body
case 1:
f() // f is not called when i == 0!
}
</pre>
<p>
But a <code>case</code> can have multiple values.
<pre>
switch i {
case 0, 1:
f() // f is called if i == 0 || i == 1.
}
</pre>
<p>
The values in a <code>case</code> need not be constants&mdash;or even integers;
any type
that supports the equality comparison operator, such as strings or
pointers, can be used&mdash;and if the <code>switch</code>
value is omitted it defaults to <code>true</code>.
<pre>
switch {
case i &lt; 0:
f1()
case i == 0:
f2()
case i &gt; 0:
f3()
}
</pre>
<p>
The <code>++</code> and <code>--</code> operators may only be used in
statements, not in expressions.
You cannot write <code>c = *p++</code>. <code>*p++</code> is parsed as
<code>(*p)++</code>.
<p>
The <code>defer</code> statement may be used to call a function after
the function containing the <code>defer</code> statement returns.
<pre>
fd := open("filename")
defer close(fd) // fd will be closed when this function returns.
</pre>
<h2 id="Constants">Constants </h2>
<p>
In Go constants may be <i>untyped</i>. This applies even to constants
named with a <code>const</code> declaration, if no
type is given in the declaration and the initializer expression uses only
untyped constants.
A value derived from an untyped constant becomes typed when it
is used within a context that
requires a typed value. This permits constants to be used relatively
freely without requiring general implicit type conversion.
<pre>
var a uint
f(a + 1) // untyped numeric constant "1" becomes typed as uint
</pre>
<p>
The language does not impose any limits on the size of an untyped
numeric constant or constant expression. A limit is only applied when
a constant is used where a type is required.
<pre>
const huge = 1 &lt;&lt; 100
f(huge &gt;&gt; 98)
</pre>
<p>
Go does not support enums. Instead, you can use the special name
<code>iota</code> in a single <code>const</code> declaration to get a
series of increasing
value. When an initialization expression is omitted for a <code>const</code>,
it reuses the preceding expression.
<pre>
const (
red = iota // red == 0
blue // blue == 1
green // green == 2
)
</pre>
<h2 id="Slices">Slices</h2>
<p>
A slice is conceptually a struct with three fields: a
pointer to an array, a length, and a capacity.
Slices support
the <code>[]</code> operator to access elements of the underlying array.
The builtin
<code>len</code> function returns the
length of the slice. The builtin <code>cap</code> function returns the
capacity.
<p>
Given an array, or another slice, a new slice is created via
<code>a[I:J]</code>. This
creates a new slice which refers to <code>a</code>, starts at
index <code>I</code>, and ends before index
<code>J</code>. It has length <code>J - I</code>.
The new slice refers to the same array
to which <code>a</code>
refers. That is, changes made using the new slice may be seen using
<code>a</code>. The
capacity of the new slice is simply the capacity of <code>a</code> minus
<code>I</code>. The capacity
of an array is the length of the array. You may also assign an array pointer
to a variable of slice type; given <code>var s []int; var a[10] int</code>,
the assignment <code>s = &amp;a</code> is equivalent to
<code>s = a[0:len(a)]</code>.
<p>
What this means is that Go uses slices for some cases where C++ uses pointers.
If you create a value of type <code>[100]byte</code> (an array of 100 bytes,
perhaps a
buffer) and you want to pass it to a function without copying it, you should
declare the function parameter to have type <code>[]byte</code>, and pass the
address
of the array. Unlike in C++, it is not
necessary to pass the length of the buffer; it is efficiently accessible via
<code>len</code>.
<p>
The slice syntax may also be used with a string. It returns a new string,
whose value is a substring of the original string.
Because strings are immutable, string slices can be implemented
without allocating new storage for the slices's contents.
<h2 id="Making_values">Making values</h2>
<p>
Go has a builtin function <code>new</code> which takes a type and
allocates space
on the heap. The allocated space will be zero-initialized for the type.
For example, <code>new(int)</code> allocates a new int on the heap,
initializes it with the value <code>0</code>,
and returns its address, which has type <code>*int</code>.
Unlike in C++, <code>new</code> is a function, not an operator;
<code>new int</code> is a syntax error.
<p>
Map and channel values must be allocated using the builtin function
<code>make</code>.
A variable declared with map or channel type without an initializer will be
automatically initialized to <code>nil</code>.
Calling <code>make(map[int]int)</code> returns a newly allocated value of
type <code>map[int]int</code>.
Note that <code>make</code> returns a value, not a pointer. This is
consistent with
the fact that map and channel values are passed by reference. Calling
<code>make</code> with
a map type takes an optional argument which is the expected capacity of the
map. Calling <code>make</code> with a channel type takes an optional
argument which sets the
buffering capacity of the channel; the default is 0 (unbuffered).
<p>
The <code>make</code> function may also be used to allocate a slice.
In this case it
allocates memory for the underlying array and returns a slice referring to it.
There is one required argument, which is the number of elements in the slice.
A second, optional, argument is the capacity of the slice. For example,
<code>make([]int, 10, 20)</code>. This is identical to
<code>new([20]int)[0:10]</code>. Since
Go uses garbage collection, the newly allocated array will be discarded
sometime after there are no references to the returned slice.
<h2 id="Interfaces">Interfaces</h2>
<p>
Where C++ provides classes, subclasses and templates,
Go provides interfaces. A
Go interface is similar to a C++ pure abstract class: a class with no
data members, with methods which are all pure virtual. However, in
Go, any type which provides the methods named in the interface may be
treated as an implementation of the interface. No explicitly declared
inheritance is required. The implementation of the interface is
entirely separate from the interface itself.
<p>
A method looks like an ordinary function definition, except that it
has a <em>receiver</em>. The receiver is similar to
the <code>this</code> pointer in a C++ class method.
<pre>
type myType struct { i int }
func (p *myType) get() int { return p.i }
</pre>
<p>
This declares a method <code>get</code> associated with <code>myType</code>.
The receiver is named <code>p</code> in the body of the function.
<p>
Methods are defined on named types. If you convert the value
to a different type, the new value will have the methods of the new type,
not the old type.
<p>
You may define methods on a builtin type by declaring a new named type
derived from it. The new type is distinct from the builtin type.
<pre>
type myInteger int
func (p myInteger) get() int { return int(p) } // Conversion required.
func f(i int) { }
var v myInteger
// f(v) is invalid.
// f(int(v)) is valid; int(v) has no defined methods.
</pre>
<p>
Given this interface:
<pre>
type myInterface interface {
get() int
set(i int)
}
</pre>
<p>
we can make <code>myType</code> satisfy the interface by adding
<pre>
func (p *myType) set(i int) { p.i = i }
</pre>
<p>
Now any function which takes <code>myInterface</code> as a parameter
will accept a
variable of type <code>*myType</code>.
<pre>
func getAndSet(x myInterface) {}
func f1() {
var p myType
getAndSet(&amp;p)
}
</pre>
<p>
In other words, if we view <code>myInterface</code> as a C++ pure abstract
base
class, defining <code>set</code> and <code>get</code> for
<code>*myType</code> made <code>*myType</code> automatically
inherit from <code>myInterface</code>. A type may satisfy multiple interfaces.
<p>
An anonymous field may be used to implement something much like a C++ child
class.
<pre>
type myChildType struct { myType; j int }
func (p *myChildType) get() int { p.j++; return p.myType.get() }
</pre>
<p>
This effectively implements <code>myChildType</code> as a child of
<code>myType</code>.
<pre>
func f2() {
var p myChildType
getAndSet(&amp;p)
}
</pre>
<p>
The <code>set</code> method is effectively inherited from
<code>myChildType</code>, because
methods associated with the anonymous field are promoted to become methods
of the enclosing type. In this case, because <code>myChildType</code> has an
anonymous field of type <code>myType</code>, the methods of
<code>myType</code> also become methods of <code>myChildType</code>.
In this example, the <code>get</code> method was
overridden, and the <code>set</code> method was inherited.
<p>
This is not precisely the same as a child class in C++.
When a method of an anonymous field is called,
its receiver is the field, not the surrounding struct.
In other words, methods on anonymous fields are not virtual functions.
When you want the equivalent of a virtual function, use an interface.
<p>
A variable which has an interface type may be converted to have a
different interface type using a special construct called a type assertion.
This is implemented dynamically
at run time, like C++ <code>dynamic_cast</code>. Unlike
<code>dynamic_cast</code>, there does
not need to be any declared relationship between the two interfaces.
<pre>
type myPrintInterface interface {
print()
}
func f3(x myInterface) {
x.(myPrintInterface).print() // type assertion to myPrintInterface
}
</pre>
<p>
The conversion to <code>myPrintInterface</code> is entirely dynamic.
It will
work as long as the underlying type of x (the <em>dynamic type</em>) defines
a <code>print</code> method.
<p>
Because the conversion is dynamic, it may be used to implement generic
programming similar to templates in C++. This is done by
manipulating values of the minimal interface.
<pre>
type Any interface { }
</pre>
<p>
Containers may be written in terms of <code>Any</code>, but the caller
must unbox using a type assertion to recover
values of the contained type. As the typing is dynamic rather
than static, there is no equivalent of the way that a C++ template may
inline the relevant operations. The operations are fully type-checked
at run time, but all operations will involve a function call.
<pre>
type iterator interface {
get() Any
set(v Any)
increment()
equal(arg *iterator) bool
}
</pre>
<h2 id="Goroutines">Goroutines</h2>
<p>
Go permits starting a new thread of execution (a <em>goroutine</em>)
using the <code>go</code>
statement. The <code>go</code> statement runs a function in a
different, newly created, goroutine.
All goroutines in a single program share the same address space.
<p>
Internally, goroutines act like coroutines that are multiplexed among
multiple operating system threads. You do not have to worry
about these details.
<pre>
func server(i int) {
for {
print(i)
sys.sleep(10)
}
}
go server(1)
go server(2)
</pre>
<p>
(Note that the <code>for</code> statement in the <code>server</code>
function is equivalent to a C++ <code>while (true)</code> loop.)
<p>
Goroutines are (intended to be) cheap.
<p>
Function literals (which Go implements as closures)
can be useful with the <code>go</code> statement.
<pre>
var g int
go func(i int) {
s := 0
for j := 0; j &lt; i; j++ { s += j }
g = s
}(1000) // Passes argument 1000 to the function literal.
</pre>
<h2 id="Channels">Channels</h2>
<p>
Channels are used to communicate between goroutines. Any value may be
sent over a channel. Channels are (intended to be) efficient and
cheap. To send a value on a channel, use <code>&lt;-</code> as a binary
operator. To
receive a value on a channel, use <code>&lt;-</code> as a unary operator.
When calling
functions, channels are passed by reference.
<p>
The Go library provides mutexes, but you can also use
a single goroutine with a shared channel.
Here is an example of using a manager function to control access to a
single value.
<pre>
type cmd struct { get bool; val int }
func manager(ch chan cmd) {
var val int = 0
for {
c := &lt;- ch
if c.get { c.val = val; ch &lt;- c }
else { val = c.val }
}
}
</pre>
<p>
In that example the same channel is used for input and output.
This is incorrect if there are multiple goroutines communicating
with the manager at once: a goroutine waiting for a response
from the manager might receive a request from another goroutine
instead.
A solution is to pass in a channel.
<pre>
type cmd2 struct { get bool; val int; ch &lt;- chan int }
func manager2(ch chan cmd2) {
var val int = 0
for {
c := &lt;- ch
if c.get { c.ch &lt;- val }
else { val = c.val }
}
}
</pre>
<p>
To use <code>manager2</code>, given a channel to it:
<pre>
func f4(ch &lt;- chan cmd2) int {
myCh := make(chan int)
c := cmd2{ true, 0, myCh } // Composite literal syntax.
ch &lt;- c
return &lt;-myCh
}
</pre>

View File

@@ -1,17 +1,4 @@
<!--{
"Title": "The Go Memory Model",
"Subtitle": "Version of March 6, 2012",
"Path": "/ref/mem"
}-->
<style>
p.rule {
font-style: italic;
}
span.event {
font-style: italic;
}
</style>
<!-- The Go Memory Model -->
<h2>Introduction</h2>
@@ -46,8 +33,8 @@ Also, if <span class="event">e<sub>1</sub></span> does not happen before <span c
after <span class="event">e<sub>2</sub></span>, then we say that <span class="event">e<sub>1</sub></span> and <span class="event">e<sub>2</sub></span> happen concurrently.
</p>
<p class="rule">
Within a single goroutine, the happens-before order is the
<p>
Within a single goroutine, the happens before order is the
order expressed by the program.
</p>
@@ -57,7 +44,7 @@ if both of the following hold:
</p>
<ol>
<li><span class="event">r</span> does not happen before <span class="event">w</span>.</li>
<li><span class="event">w</span> happens before <span class="event">r</span>.</li>
<li>There is no other write <span class="event">w'</span> to <code>v</code> that happens
after <span class="event">w</span> but before <span class="event">r</span>.</li>
</ol>
@@ -107,9 +94,9 @@ unspecified order.
<h3>Initialization</h3>
<p>
Program initialization runs in a single goroutine,
but that goroutine may create other goroutines,
which run concurrently.
Program initialization runs in a single goroutine and
new goroutines created during initialization do not
start running until initialization ends.
</p>
<p class="rule">
@@ -122,6 +109,11 @@ The start of the function <code>main.main</code> happens after
all <code>init</code> functions have finished.
</p>
<p class="rule">
The execution of any goroutines created during <code>init</code>
functions happens after all <code>init</code> functions have finished.
</p>
<h3>Goroutine creation</h3>
<p class="rule">
@@ -221,17 +213,6 @@ the corresponding receive on <code>c</code> completes, which happens before
the <code>print</code>.
</p>
<p class="rule">
The closing of a channel happens before a receive that returns a zero value
because the channel is closed.
</p>
<p>
In the previous example, replacing
<code>c &lt;- 0</code> with <code>close(c)</code>
yields a program with the same guaranteed behavior.
</p>
<p class="rule">
A receive from an unbuffered channel happens before
the send on that channel completes.
@@ -283,7 +264,7 @@ The <code>sync</code> package implements two lock data types,
<p class="rule">
For any <code>sync.Mutex</code> or <code>sync.RWMutex</code> variable <code>l</code> and <i>n</i> &lt; <i>m</i>,
call <i>n</i> of <code>l.Unlock()</code> happens before call <i>m</i> of <code>l.Lock()</code> returns.
the <i>n</i>'th call to <code>l.Unlock()</code> happens before the <i>m</i>'th call to <code>l.Lock()</code> returns.
</p>
<p>
@@ -316,9 +297,9 @@ which happens before the <code>print</code>.
<p class="rule">
For any call to <code>l.RLock</code> on a <code>sync.RWMutex</code> variable <code>l</code>,
there is an <i>n</i> such that the <code>l.RLock</code> happens (returns) after call <i>n</i> to
there is an <i>n</i> such that the <code>l.RLock</code> happens (returns) after the <i>n</i>'th call to
<code>l.Unlock</code> and the matching <code>l.RUnlock</code> happens
before call <i>n</i>+1 to <code>l.Lock</code>.
before the <i>n</i>+1'th call to <code>l.Lock</code>.
</p>
<h3>Once</h3>

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