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doc: update "How to Write Go Code" to use the go tool
R=golang-dev, r, kevlar, rsc CC=golang-dev https://golang.org/cl/5534045
This commit is contained in:
Andrew Gerrand
parent
014c342b1e
commit
d9b82baac1
327
doc/code.html
327
doc/code.html
@ -45,120 +45,89 @@ that receives a message summarizing each checkin to the Go repository.
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<h2 id="New_package">Creating a new package</h2>
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<h3>Choosing an import path</h3>
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<p>
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The source code for the package with import path
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<code>x/y</code> is, by convention, kept in the
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directory <code>$GOROOT/src/pkg/x/y</code>.
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The standard packages are given short names like <code>fmt</code> and
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<code>net/http</code> for convenience.
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For your own projects, choose a name space that is unlikely
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to collide with future additions to the standard library or other
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external libraries.
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</p>
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<h3>Makefile</h3>
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<p>
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For instance, if your source repository is at <code>example.com</code>
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or <code>code.google.com/p/example</code>, you should begin your package
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paths with that URL, as in "<code>example.com/foo/bar</code>" or
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"<code>code.google.com/p/example/foo/bar</code>".
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This way the <a href="/cmd/go/"><code>go</code> tool</a> can automatically
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check out and build the source code from its import path.
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</p>
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<p>
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It would be nice to have Go-specific tools that
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inspect the source files to determine what to build and in
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what order, but for now, Go uses GNU <code>make</code>.
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Thus, the first file to create in a new package directory is
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usually the <code>Makefile</code>.
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The basic form used in the Go source tree
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is illustrated by <a href="../src/pkg/container/vector/Makefile"><code>src/pkg/container/vector/Makefile</code></a>:
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If you don't intend your code to be installed in this way, you should at
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least use a unique prefix like "<code>widgets/</code>", as in
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"<code>widgets/foo/bar</code>". A good rule is to use a prefix such as your
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company or project name since it is unlikely to be used by another group.
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</p>
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<h3>The <code>go</code> tool and <code>GOPATH</code></h3>
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<p>
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The <a href="/cmd/go/"><code>go</code> tool</a> is the standard means of
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building and installing Go libraries and programs. It is a "zero configuration"
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tool; it determines how to build Go packages from their source code alone.
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</p>
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<p>
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To use the <code>go</code> tool effectively you must set the
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<code>GOPATH</code> variable.
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<code>GOPATH</code> specifies a list of paths that contain Go source code
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and package binaries. Source code, package objects, and command binaries are
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located inside the <code>GOPATH</code>s' <code>src</code>, <code>pkg</code>,
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and <code>bin</code> subdirectories respectively.
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</p>
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<p>
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You should set <code>GOPATH</code> in your shell profile
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(<code>$HOME/.bashrc</code>, <code>$HOME/.profile</code>, or equivalent).
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</p>
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<p>
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This shell session demonstrates setting <code>GOPATH</code>, creating a trivial
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<code>widgets/foo</code> package, and building and installing the package.
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</p>
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<pre>
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include ../../../Make.inc
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TARG=container/vector
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GOFILES=\
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intvector.go\
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stringvector.go\
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vector.go\
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include ../../../Make.pkg
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$ export GOPATH=$HOME/gocode
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$ mkdir -p $GOPATH/src/widgets/foo
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$ cat > $GOPATH/src/widgets/foo/foo.go
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package foo
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const String = "Go rules!"
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^D
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$ go install widgets/foo
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$ ls $GOPATH/pkg/*/example
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foo.a
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</pre>
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<p>
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Outside the Go source tree (for personal packages), the standard form is
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</p>
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<pre>
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include $(GOROOT)/src/Make.inc
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TARG=mypackage
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GOFILES=\
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my1.go\
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my2.go\
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include $(GOROOT)/src/Make.pkg
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</pre>
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<p>(<code>^D</code> means to type Control-D.)</p>
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<p>
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The first and last lines <code>include</code> standard definitions and rules.
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Packages maintained in the standard Go tree use a relative path (instead of
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<code>$(GOROOT)/src</code>) so that <code>make</code> will work correctly
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even if <code>$(GOROOT)</code> contains spaces.
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This makes it easy for programmers to try Go.
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</p>
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<p>
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If you have not set <code>$GOROOT</code> in your environment,
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you must run <code>gomake</code> to use this form of makefile.
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<code>Gomake</code> also takes care to invoke GNU Make
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even on systems where it is installed as <code>gmake</code>
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rather than <code>make</code>.
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</p>
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<p>
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<code>TARG</code> is the target install path for the package,
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the string that clients will use to import it.
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Inside the Go tree, this string should be the same as the directory
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in which the <code>Makefile</code> appears, with the
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<code>$GOROOT/src/pkg/</code> prefix removed.
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Outside the Go tree, you can use any <code>TARG</code> you
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want that doesn't conflict with the standard Go package names.
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A common convention is to use an identifying top-level name
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to group your packages: <code>myname/tree</code>, <code>myname/filter</code>, etc.
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Note that even if you keep your package source outside the
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Go tree, running <code>make install</code> installs your
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package binaries in the standard location—<code>$GOROOT/pkg</code>—to
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make it easy to find them.
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</p>
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<p>
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<code>GOFILES</code> is a list of source files to compile to
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create the package. The trailing <code>\</code> characters
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allow the list to be split onto multiple lines
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for easy sorting.
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</p>
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<p>
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If you create a new package directory in the Go tree, add it to the list in
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<code>$GOROOT/src/pkg/Makefile</code> so that it
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is included in the standard build. Then run:
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<pre>
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cd $GOROOT/src/pkg
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./deps.bash
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</pre>
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<p>
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to update the dependency file <code>Make.deps</code>.
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(This happens automatically each time you run <code>all.bash</code>
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or <code>make.bash</code>.)
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</p>
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<p>
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If you change the imports of an existing package,
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you do not need to edit <code>$GOROOT/src/pkg/Makefile</code>
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but you will still need to run <code>deps.bash</code> as above.
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Type <code>go help gopath</code> on the command line for more information
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about <code>GOPATH</code>.
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</p>
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<h3>Go source files</h3>
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<p>
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The first statement in each of the source files listed in the <code>Makefile</code>
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should be <code>package <i>name</i></code>, where <code><i>name</i></code>
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is the package's default name for imports.
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The first statement in a Go source file should be <code>package
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<i>name</i></code>, where <code><i>name</i></code> is the package's default
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name for imports.
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(All files in a package must use the same <code><i>name</i></code>.)
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Go's convention is that the package name is the last element of the
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import path: the package imported as <code>"crypto/rot13"</code>
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import path: the package imported as "<code>crypto/rot13</code>"
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should be named <code>rot13</code>.
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There is no requirement that package names be unique
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across all packages linked into a single binary,
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@ -178,63 +147,81 @@ that topic.
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</p>
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<h2 id="Building_programs">Building programs</h2>
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<p>To build a Go program with gomake, create a Makefile alongside your program's
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source files. It should be similar to the example above, but include
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<code>Make.cmd</code> instead of <code>Make.pkg</code>:
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<pre>
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include $(GOROOT)/src/Make.inc
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TARG=helloworld
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GOFILES=\
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helloworld.go\
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include $(GOROOT)/src/Make.cmd
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</pre>
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<p>Running <code>gomake</code> will compile <code>helloworld.go</code>
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and produce an executable named <code>helloworld</code> in the current
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directory.
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<p>
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The <a href="/cmd/go/"><code>go</code> tool</a> treats code belonging to
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<code>package main</code> as an executable command, and installs the package
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binary to the <code>GOPATH</code>'s <code>bin</code> subdirectory.
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</p>
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<p>
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Running <code>gomake install</code> will build <code>helloworld</code> if
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necessary and copy it to the <code>$GOBIN</code> directory
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(<code>$GOROOT/bin/</code> is the default).
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Building executable commands is the same as building packages.
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Use "<code>go install</code>":
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</p>
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<pre>
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$ cat > $GOPATH/src/widgets/bar/bar.go
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package main
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import (
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"fmt"
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"widgets/foo"
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)
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func main() {
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fmt.Println(foo.String)
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}
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^D
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$ go install widgets/bar
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$ $GOPATH/bin/bar
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Go rules!
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</pre>
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<p>
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Run <code>go help build</code> and <code>go help install</code> for more
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about building and installing Go binaries.
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</p>
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<h2 id="Testing">Testing</h2>
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<p>
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Go has a lightweight test framework known as <code>gotest</code>.
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Go has a lightweight test framework composed of the <code>go</code> tool and
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the <code>testing</code> package.
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You write a test by creating a file with a name ending in <code>_test.go</code>
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that contains functions named <code>TestXXX</code> with signature <code>func (t *testing.T)</code>.
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that contains functions named <code>TestXXX</code> with signature
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<code>func (t *testing.T)</code>.
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The test framework runs each such function;
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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.
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The <a href="/cmd/gotest/">gotest command documentation</a>
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and the <a href="/pkg/testing/">testing package documentation</a> give more detail.
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if the function calls a failure function such as <code>t.Error</code> or
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<code>t.Fail</code>, the test is considered to have failed.
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Run <code>go help test</code> and see the
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<a href="/pkg/testing/">testing package documentation</a> for more detail.
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</p>
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<p>
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The <code>*_test.go</code> files should not be listed in the <code>Makefile</code>.
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To run the test, run "<code>go test</code>":
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</p>
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<p>
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To run the test, run either <code>make test</code> or <code>gotest</code>
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(they are equivalent).
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To run only the tests in a single test file, for instance <code>one_test.go</code>,
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run <code>gotest one_test.go</code>.
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</p>
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<pre>
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$ cat > $GOPATH/src/widgets/foo/foo_test.go
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package foo
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import "testing"
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func TestString(t *testing.T) {
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const expect = "Go rules!"
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if String != expect {
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t.Errorf("String == %q, want %q", String, expect)
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}
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}
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^D
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$ go test widgets/foo
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ok widgets/foo
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</pre>
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<p>
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If your change affects performance, add a <code>Benchmark</code> function
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(see the <a href="/cmd/gotest/">gotest command documentation</a>)
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and run it using <code>gotest -test.bench=.</code>.
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</p>
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<p>
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Once your new code is tested and working,
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it's time to get it <a href="contribute.html">reviewed and submitted</a>.
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(run <code>go help testfunc</code>) and run it using <code>go test
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-test.bench=.*</code>.
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</p>
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<h2 id="pkg_example">An example package with tests</h2>
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@ -242,7 +229,7 @@ it's time to get it <a href="contribute.html">reviewed and submitted</a>.
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<p>
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This example package, <code>numbers</code>, consists of the function
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<code>Double</code>, which takes an <code>int</code> and returns that value
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multiplied by 2. It consists of three files.
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multiplied by 2. It consists of two files.
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</p>
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<p>
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@ -289,38 +276,24 @@ func TestDouble(t *testing.T) {
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</pre>
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<p>
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Finally, the <code>Makefile</code>:
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</p>
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<pre>
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include $(GOROOT)/src/Make.inc
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TARG=numbers
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GOFILES=\
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numbers.go\
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include $(GOROOT)/src/Make.pkg
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</pre>
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<p>
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Running <code>gomake install</code> will build and install the package to
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the <code>$GOROOT/pkg/</code> directory (it can then be used by any
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program on the system).
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Running <code>go install</code> will build and install the package to
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the <code>GOPATH</code>'s <code>pkg</code> directory
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(it can then be imported by any other Go program).
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</p>
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<p>
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Running <code>gomake test</code> (or just running the command
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<code>gotest</code>) will rebuild the package, including the
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Running <code>go test</code> will rebuild the package, including the
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<code>numbers_test.go</code> file, and then run the <code>TestDouble</code>
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function. The output "<code>PASS</code>" indicates that all tests passed
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function. The output "<code>ok</code>" indicates that all tests passed
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successfully. Breaking the implementation by changing the multiplier from
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<code>2</code> to <code>3</code> will allow you to see how failing tests are
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reported.
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</p>
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<p>
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See the <a href="/cmd/gotest/">gotest documentation</a> and the
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<a href="/pkg/testing/">testing package</a> for more detail.
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Run <code>go help test</code>, <code>go help testfunc</code>,
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and <code>go help testflag</code> and see the
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<a href="/pkg/testing/">testing package documentation</a> for more detail.
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</p>
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<h2 id="arch_os_specific">Architecture- and operating system-specific code</h2>
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@ -335,34 +308,34 @@ different operating systems.</p>
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<p>To compile such code, use the <code>$GOOS</code> and <code>$GOARCH</code>
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<a href="/doc/install.html#environment">environment variables</a> in your
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source file names and <code>Makefile</code>.</p>
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source file names.</p>
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<p>For example, this <code>Makefile</code> describes a package that builds on
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<p>For example, consider the package <code>foo</code> that consists of four
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files:</p>
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<pre>
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foo.go
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foo_386.go
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foo_amd64.go
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foo_arm.go
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</pre>
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describes a package that builds on
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different operating systems by parameterizing the file name with
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<code>$GOOS</code>.</p>
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<pre>
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include $(GOROOT)/src/Make.inc
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<p>The general code goes in <code>foo.go</code>, while architecture-specific
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code goes in <code>foo_386.go</code>, <code>foo_amd64.go</code>, and
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<code>foo_arm.go</code>.</p>
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TARG=mypackage
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GOFILES=\
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my.go\
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my_$(GOOS).go\
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include $(GOROOT)/src/Make.pkg
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</pre>
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<p>The OS-specific code goes in <code>my_linux.go</code>,
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<code>my_darwin.go</code>, and so on.</p>
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<p>If you follow these conventional parameterizations, tools such as
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<a href="/cmd/goinstall/">goinstall</a> will work seamlessly with your package:
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</p>
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<p>If you follow these conventional parameterizations, tools such as the <a
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href="/cmd/go/"><code>go</code> tool</a> will work seamlessly with your
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package:</p>
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<pre>
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my_$(GOOS).go
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my_$(GOARCH).go
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my_$(GOOS)_$(GOARCH).go
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foo_$GOOS.go
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foo_$GOARCH.go
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foo_$GOOS_$GOARCH.go
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</pre>
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<p>The same holds for <code>.s</code> (assembly) files.</p>
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<p>The same holds for <code>.s</code> (assembly) and <code>.c</code> files.</p>
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