mirror of
https://github.com/golang/go
synced 2024-11-26 21:01:31 -07:00
369 lines
10 KiB
HTML
369 lines
10 KiB
HTML
<!-- How to Write Go Code -->
|
|
|
|
<h2 id="Introduction">Introduction</h2>
|
|
|
|
<p>
|
|
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>
|
|
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>
|
|
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>
|
|
include ../../../Make.inc
|
|
|
|
TARG=container/vector
|
|
GOFILES=\
|
|
intvector.go\
|
|
stringvector.go\
|
|
vector.go\
|
|
|
|
include ../../../Make.pkg
|
|
</pre>
|
|
|
|
<p>
|
|
Outside the Go source tree (for personal packages), the standard form is
|
|
</p>
|
|
|
|
<pre>
|
|
include $(GOROOT)/src/Make.inc
|
|
|
|
TARG=mypackage
|
|
GOFILES=\
|
|
my1.go\
|
|
my2.go\
|
|
|
|
include $(GOROOT)/src/Make.pkg
|
|
</pre>
|
|
|
|
<p>
|
|
The first and last lines <code>include</code> standard definitions and rules.
|
|
Packages maintained in the standard Go tree use a relative path (instead of
|
|
<code>$(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>$GOROOT/src/pkg/</code> prefix removed.
|
|
Outside the Go tree, you can use any <code>TARG</code> you
|
|
want that doesn't conflict with the standard Go package names.
|
|
A common convention is to use an identifying top-level name
|
|
to group your packages: <code>myname/tree</code>, <code>myname/filter</code>, etc.
|
|
Note that even if you keep your package source outside the
|
|
Go tree, running <code>make install</code> installs your
|
|
package binaries in the standard location—<code>$GOROOT/pkg</code>—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>
|
|
cd $GOROOT/src/pkg
|
|
./deps.bash
|
|
</pre>
|
|
<p>
|
|
to update the dependency file <code>Make.deps</code>.
|
|
(This happens automatically each time you run <code>all.bash</code>
|
|
or <code>make.bash</code>.)
|
|
</p>
|
|
|
|
<p>
|
|
If you change the imports of an existing package,
|
|
you do not need to edit <code>$GOROOT/src/pkg/Makefile</code>
|
|
but you will still need to run <code>deps.bash</code> as above.
|
|
</p>
|
|
|
|
|
|
<h3>Go source files</h3>
|
|
|
|
<p>
|
|
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>.)
|
|
Go's convention is that the package name is the last element of the
|
|
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,
|
|
only that the import paths (their full file names) be unique.
|
|
</p>
|
|
|
|
<p>
|
|
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>
|
|
include $(GOROOT)/src/Make.inc
|
|
|
|
TARG=helloworld
|
|
GOFILES=\
|
|
helloworld.go\
|
|
|
|
include $(GOROOT)/src/Make.cmd
|
|
</pre>
|
|
|
|
<p>Running <code>gomake</code> will compile <code>helloworld.go</code>
|
|
and produce an executable named <code>helloworld</code> in the current
|
|
directory.
|
|
</p>
|
|
|
|
<p>
|
|
Running <code>gomake install</code> will build <code>helloworld</code> if
|
|
necessary and copy it to the <code>$GOBIN</code> directory
|
|
(<code>$GOROOT/bin/</code> is the default).
|
|
</p>
|
|
|
|
<h2 id="Testing">Testing</h2>
|
|
|
|
<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>.
|
|
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.
|
|
The <a href="/cmd/gotest/">gotest command documentation</a>
|
|
and the <a href="/pkg/testing/">testing package documentation</a> give more detail.
|
|
</p>
|
|
|
|
<p>
|
|
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 numbers
|
|
|
|
func Double(i int) int {
|
|
return i * 2
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
Next, the tests, <code>numbers_test.go</code>:
|
|
</p>
|
|
|
|
<pre>
|
|
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>
|
|
Finally, the <code>Makefile</code>:
|
|
</p>
|
|
|
|
<pre>
|
|
include $(GOROOT)/src/Make.inc
|
|
|
|
TARG=numbers
|
|
GOFILES=\
|
|
numbers.go\
|
|
|
|
include $(GOROOT)/src/Make.pkg
|
|
</pre>
|
|
|
|
<p>
|
|
Running <code>gomake install</code> will build and install the package to
|
|
the <code>$GOROOT/pkg/</code> directory (it can then be used by any
|
|
program on the system).
|
|
</p>
|
|
|
|
<p>
|
|
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 $(GOROOT)/src/Make.pkg
|
|
</pre>
|
|
|
|
<p>The OS-specific code goes in <code>my_linux.go</code>,
|
|
<code>my_darwin.go</code>, and so on.</p>
|
|
|
|
<p>If you follow these conventional parameterizations, tools such as
|
|
<a href="/cmd/goinstall/">goinstall</a> will work seamlessly with your package:
|
|
</p>
|
|
|
|
<pre>
|
|
my_$(GOOS).go
|
|
my_$(GOARCH).go
|
|
my_$(GOOS)_$(GOARCH).go
|
|
</pre>
|
|
|
|
<p>The same holds for <code>.s</code> (assembly) files.</p>
|