mirror of
https://github.com/golang/go
synced 2024-09-05 07:54:46 +00:00
![Russ Cox](/assets/img/avatar_default.png)
It's already half gone and later will be all gone. It's not worth explaining in an introduction doc. Fixes #24506 Updates #4719 Change-Id: Ie48128b3aa090d84e0e734aa45f14a4480292913 Reviewed-on: https://go-review.googlesource.com/129679 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
649 lines
16 KiB
HTML
649 lines
16 KiB
HTML
<!--{
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"Title": "How to Write Go Code"
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}-->
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<h2 id="Introduction">Introduction</h2>
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<p>
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This document demonstrates the development of a simple Go package and
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introduces the <a href="/cmd/go/">go tool</a>, the standard way to fetch,
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build, and install Go packages and commands.
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</p>
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<p>
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The <code>go</code> tool requires you to organize your code in a specific
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way. Please read this document carefully.
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It explains the simplest way to get up and running with your Go installation.
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</p>
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<p>
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A similar explanation is available as a
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<a href="//www.youtube.com/watch?v=XCsL89YtqCs">screencast</a>.
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</p>
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<h2 id="Organization">Code organization</h2>
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<h3 id="Overview">Overview</h3>
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<ul>
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<li>Go programmers typically keep all their Go code in a single <i>workspace</i>.</li>
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<li>A workspace contains many version control <i>repositories</i>
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(managed by Git, for example).</li>
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<li>Each repository contains one or more <i>packages</i>.</li>
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<li>Each package consists of one or more Go source files in a single directory.</li>
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<li>The path to a package's directory determines its <i>import path</i>.</li>
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</ul>
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<p>
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Note that this differs from other programming environments in which every
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project has a separate workspace and workspaces are closely tied to version
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control repositories.
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</p>
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<h3 id="Workspaces">Workspaces</h3>
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<p>
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A workspace is a directory hierarchy with two directories at its root:
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</p>
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<ul>
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<li><code>src</code> contains Go source files, and
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<li><code>bin</code> contains executable commands.
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</ul>
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<p>
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The <code>go</code> tool builds and installs binaries to the <code>bin</code> directory.
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</p>
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<p>
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The <code>src</code> subdirectory typically contains multiple version control
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repositories (such as for Git or Mercurial) that track the development of one
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or more source packages.
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</p>
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<p>
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To give you an idea of how a workspace looks in practice, here's an example:
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</p>
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<pre>
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bin/
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hello # command executable
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outyet # command executable
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src/
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<a href="https://github.com/golang/example/">github.com/golang/example/</a>
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.git/ # Git repository metadata
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hello/
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hello.go # command source
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outyet/
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main.go # command source
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main_test.go # test source
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stringutil/
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reverse.go # package source
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reverse_test.go # test source
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<a href="https://golang.org/x/image/">golang.org/x/image/</a>
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.git/ # Git repository metadata
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bmp/
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reader.go # package source
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writer.go # package source
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... (many more repositories and packages omitted) ...
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</pre>
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<p>
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The tree above shows a workspace containing two repositories
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(<code>example</code> and <code>image</code>).
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The <code>example</code> repository contains two commands (<code>hello</code>
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and <code>outyet</code>) and one library (<code>stringutil</code>).
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The <code>image</code> repository contains the <code>bmp</code> package
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and <a href="https://godoc.org/golang.org/x/image">several others</a>.
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</p>
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<p>
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A typical workspace contains many source repositories containing many
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packages and commands. Most Go programmers keep <i>all</i> their Go source code
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and dependencies in a single workspace.
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</p>
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<p>
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Note that symbolic links should <b>not</b> be used to link files or directories into your workspace.
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</p>
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<p>
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Commands and libraries are built from different kinds of source packages.
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We will discuss the distinction <a href="#PackageNames">later</a>.
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</p>
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<h3 id="GOPATH">The <code>GOPATH</code> environment variable</h3>
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<p>
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The <code>GOPATH</code> environment variable specifies the location of your
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workspace. It defaults to a directory named <code>go</code> inside your home directory,
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so <code>$HOME/go</code> on Unix,
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<code>$home/go</code> on Plan 9,
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and <code>%USERPROFILE%\go</code> (usually <code>C:\Users\YourName\go</code>) on Windows.
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</p>
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<p>
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If you would like to work in a different location, you will need to
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<a href="https://golang.org/wiki/SettingGOPATH">set <code>GOPATH</code></a>
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to the path to that directory.
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(Another common setup is to set <code>GOPATH=$HOME</code>.)
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Note that <code>GOPATH</code> must <b>not</b> be the
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same path as your Go installation.
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</p>
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<p>
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The command <code>go</code> <code>env</code> <code>GOPATH</code>
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prints the effective current <code>GOPATH</code>;
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it prints the default location if the environment variable is unset.
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</p>
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<p>
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For convenience, add the workspace's <code>bin</code> subdirectory
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to your <code>PATH</code>:
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</p>
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<pre>
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$ <b>export PATH=$PATH:$(go env GOPATH)/bin</b>
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</pre>
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<p>
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The scripts in the rest of this document use <code>$GOPATH</code>
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instead of <code>$(go env GOPATH)</code> for brevity.
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To make the scripts run as written
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if you have not set GOPATH,
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you can substitute $HOME/go in those commands
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or else run:
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</p>
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<pre>
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$ <b>export GOPATH=$(go env GOPATH)</b>
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</pre>
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<p>
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To learn more about the <code>GOPATH</code> environment variable, see
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<a href="/cmd/go/#hdr-GOPATH_environment_variable"><code>'go help gopath'</code></a>.
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</p>
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<p>
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To use a custom workspace location,
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<a href="https://golang.org/wiki/SettingGOPATH">set the <code>GOPATH</code> environment variable</a>.
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</p>
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<h3 id="ImportPaths">Import paths</h3>
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<p>
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An <i>import path</i> is a string that uniquely identifies a package.
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A package's import path corresponds to its location inside a workspace
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or in a remote repository (explained below).
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</p>
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<p>
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The packages from the standard library are given short import paths such as
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<code>"fmt"</code> and <code>"net/http"</code>.
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For your own packages, you must choose a base path that is unlikely to
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collide with future additions to the standard library or other external
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libraries.
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</p>
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<p>
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If you keep your code in a source repository somewhere, then you should use the
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root of that source repository as your base path.
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For instance, if you have a <a href="https://github.com/">GitHub</a> account at
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<code>github.com/user</code>, that should be your base path.
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</p>
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<p>
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Note that you don't need to publish your code to a remote repository before you
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can build it. It's just a good habit to organize your code as if you will
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publish it someday. In practice you can choose any arbitrary path name,
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as long as it is unique to the standard library and greater Go ecosystem.
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</p>
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<p>
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We'll use <code>github.com/user</code> as our base path. Create a directory
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inside your workspace in which to keep source code:
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</p>
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<pre>
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$ <b>mkdir -p $GOPATH/src/github.com/user</b>
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</pre>
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<h3 id="Command">Your first program</h3>
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<p>
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To compile and run a simple program, first choose a package path (we'll use
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<code>github.com/user/hello</code>) and create a corresponding package directory
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inside your workspace:
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</p>
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<pre>
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$ <b>mkdir $GOPATH/src/github.com/user/hello</b>
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</pre>
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<p>
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Next, create a file named <code>hello.go</code> inside that directory,
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containing the following Go code.
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</p>
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<pre>
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package main
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import "fmt"
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func main() {
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fmt.Println("Hello, world.")
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}
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</pre>
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<p>
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Now you can build and install that program with the <code>go</code> tool:
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</p>
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<pre>
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$ <b>go install github.com/user/hello</b>
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</pre>
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<p>
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Note that you can run this command from anywhere on your system. The
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<code>go</code> tool finds the source code by looking for the
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<code>github.com/user/hello</code> package inside the workspace specified by
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<code>GOPATH</code>.
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</p>
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<p>
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You can also omit the package path if you run <code>go install</code> from the
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package directory:
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</p>
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<pre>
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$ <b>cd $GOPATH/src/github.com/user/hello</b>
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$ <b>go install</b>
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</pre>
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<p>
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This command builds the <code>hello</code> command, producing an executable
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binary. It then installs that binary to the workspace's <code>bin</code>
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directory as <code>hello</code> (or, under Windows, <code>hello.exe</code>).
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In our example, that will be <code>$GOPATH/bin/hello</code>, which is
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<code>$HOME/go/bin/hello</code>.
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</p>
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<p>
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The <code>go</code> tool will only print output when an error occurs, so if
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these commands produce no output they have executed successfully.
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</p>
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<p>
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You can now run the program by typing its full path at the command line:
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</p>
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<pre>
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$ <b>$GOPATH/bin/hello</b>
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Hello, world.
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</pre>
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<p>
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Or, as you have added <code>$GOPATH/bin</code> to your <code>PATH</code>,
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just type the binary name:
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</p>
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<pre>
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$ <b>hello</b>
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Hello, world.
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</pre>
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<p>
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If you're using a source control system, now would be a good time to initialize
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a repository, add the files, and commit your first change. Again, this step is
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optional: you do not need to use source control to write Go code.
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</p>
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<pre>
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$ <b>cd $GOPATH/src/github.com/user/hello</b>
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$ <b>git init</b>
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Initialized empty Git repository in /home/user/work/src/github.com/user/hello/.git/
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$ <b>git add hello.go</b>
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$ <b>git commit -m "initial commit"</b>
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[master (root-commit) 0b4507d] initial commit
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1 file changed, 1 insertion(+)
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create mode 100644 hello.go
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</pre>
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<p>
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Pushing the code to a remote repository is left as an exercise for the reader.
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</p>
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<h3 id="Library">Your first library</h3>
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<p>
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Let's write a library and use it from the <code>hello</code> program.
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</p>
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<p>
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Again, the first step is to choose a package path (we'll use
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<code>github.com/user/stringutil</code>) and create the package directory:
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</p>
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<pre>
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$ <b>mkdir $GOPATH/src/github.com/user/stringutil</b>
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</pre>
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<p>
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Next, create a file named <code>reverse.go</code> in that directory with the
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following contents.
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</p>
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<pre>
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// Package stringutil contains utility functions for working with strings.
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package stringutil
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// Reverse returns its argument string reversed rune-wise left to right.
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func Reverse(s string) string {
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r := []rune(s)
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for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
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r[i], r[j] = r[j], r[i]
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}
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return string(r)
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}
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</pre>
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<p>
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Now, test that the package compiles with <code>go build</code>:
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</p>
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<pre>
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$ <b>go build github.com/user/stringutil</b>
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</pre>
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<p>
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Or, if you are working in the package's source directory, just:
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</p>
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<pre>
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$ <b>go build</b>
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</pre>
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<p>
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This won't produce an output file.
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Instead it saves the compiled package in the local build cache.
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</p>
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<p>
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After confirming that the <code>stringutil</code> package builds,
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modify your original <code>hello.go</code> (which is in
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<code>$GOPATH/src/github.com/user/hello</code>) to use it:
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</p>
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<pre>
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package main
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import (
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"fmt"
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<b>"github.com/user/stringutil"</b>
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)
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func main() {
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fmt.Println(stringutil.Reverse("!oG ,olleH"))
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}
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</pre>
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<p>
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Install the <code>hello</code> program:
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</p>
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<pre>
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$ <b>go install github.com/user/hello</b>
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</pre>
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<p>
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Running the new version of the program, you should see a new, reversed message:
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</p>
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<pre>
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$ <b>hello</b>
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Hello, Go!
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</pre>
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<p>
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After the steps above, your workspace should look like this:
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</p>
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<pre>
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bin/
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hello # command executable
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src/
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github.com/user/
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hello/
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hello.go # command source
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stringutil/
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reverse.go # package source
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</pre>
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<h3 id="PackageNames">Package names</h3>
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<p>
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The first statement in a Go source file must be
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</p>
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<pre>
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package <i>name</i>
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</pre>
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<p>
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where <code><i>name</i></code> is the package's default 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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</p>
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<p>
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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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should be named <code>rot13</code>.
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</p>
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<p>
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Executable commands must always use <code>package main</code>.
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</p>
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<p>
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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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only that the import paths (their full file names) be unique.
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</p>
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<p>
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See <a href="/doc/effective_go.html#names">Effective Go</a> to learn more about
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Go's naming conventions.
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</p>
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<h2 id="Testing">Testing</h2>
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|
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<p>
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Go has a lightweight test framework composed of the <code>go test</code>
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command and the <code>testing</code> package.
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</p>
|
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<p>
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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
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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
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<code>t.Fail</code>, the test is considered to have failed.
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</p>
|
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<p>
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Add a test to the <code>stringutil</code> package by creating the file
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<code>$GOPATH/src/github.com/user/stringutil/reverse_test.go</code> containing
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the following Go code.
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</p>
|
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<pre>
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package stringutil
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import "testing"
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func TestReverse(t *testing.T) {
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cases := []struct {
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in, want string
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}{
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{"Hello, world", "dlrow ,olleH"},
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{"Hello, 世界", "界世 ,olleH"},
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{"", ""},
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}
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for _, c := range cases {
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got := Reverse(c.in)
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if got != c.want {
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t.Errorf("Reverse(%q) == %q, want %q", c.in, got, c.want)
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}
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}
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}
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</pre>
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<p>
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Then run the test with <code>go test</code>:
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</p>
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|
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<pre>
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$ <b>go test github.com/user/stringutil</b>
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ok github.com/user/stringutil 0.165s
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</pre>
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<p>
|
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As always, if you are running the <code>go</code> tool from the package
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directory, you can omit the package path:
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</p>
|
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|
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<pre>
|
|
$ <b>go test</b>
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ok github.com/user/stringutil 0.165s
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</pre>
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|
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<p>
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Run <code><a href="/cmd/go/#hdr-Test_packages">go help test</a></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="remote">Remote packages</h2>
|
|
|
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<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> tool uses
|
|
this property to automatically fetch packages from remote repositories.
|
|
For instance, the examples described in this document are also kept in a
|
|
Git repository hosted at GitHub
|
|
<code><a href="https://github.com/golang/example">github.com/golang/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:
|
|
</p>
|
|
|
|
<pre>
|
|
$ <b>go get github.com/golang/example/hello</b>
|
|
$ <b>$GOPATH/bin/hello</b>
|
|
Hello, Go examples!
|
|
</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>.)
|
|
</p>
|
|
|
|
<p>
|
|
After issuing the above <code>go get</code> command, the workspace directory
|
|
tree should now look like this:
|
|
</p>
|
|
|
|
<pre>
|
|
bin/
|
|
hello # command executable
|
|
src/
|
|
github.com/golang/example/
|
|
.git/ # Git repository metadata
|
|
hello/
|
|
hello.go # command source
|
|
stringutil/
|
|
reverse.go # package source
|
|
reverse_test.go # test source
|
|
github.com/user/
|
|
hello/
|
|
hello.go # command source
|
|
stringutil/
|
|
reverse.go # package source
|
|
reverse_test.go # test source
|
|
</pre>
|
|
|
|
<p>
|
|
The <code>hello</code> command hosted at GitHub depends on the
|
|
<code>stringutil</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 "github.com/golang/example/stringutil"
|
|
</pre>
|
|
|
|
<p>
|
|
This convention is the easiest way to make your Go packages available for
|
|
others to use.
|
|
The <a href="//golang.org/wiki/Projects">Go Wiki</a>
|
|
and <a href="//godoc.org/">godoc.org</a>
|
|
provide lists of external Go projects.
|
|
</p>
|
|
|
|
<p>
|
|
For more information on using remote repositories with the <code>go</code> tool, see
|
|
<code><a href="/cmd/go/#hdr-Remote_import_paths">go help importpath</a></code>.
|
|
</p>
|
|
|
|
|
|
<h2 id="next">What's next</h2>
|
|
|
|
<p>
|
|
Subscribe to the
|
|
<a href="//groups.google.com/group/golang-announce">golang-announce</a>
|
|
mailing list to be notified when a new stable version of Go is released.
|
|
</p>
|
|
|
|
<p>
|
|
See <a href="/doc/effective_go.html">Effective Go</a> for tips on writing
|
|
clear, idiomatic Go code.
|
|
</p>
|
|
|
|
<p>
|
|
Take <a href="//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>
|
|
|
|
|
|
<h2 id="help">Getting help</h2>
|
|
|
|
<p>
|
|
For real-time help, ask the helpful gophers in <code>#go-nuts</code> on the
|
|
<a href="https://freenode.net/">Freenode</a> IRC server.
|
|
</p>
|
|
|
|
<p>
|
|
The official mailing list for discussion of the Go language is
|
|
<a href="//groups.google.com/group/golang-nuts">Go Nuts</a>.
|
|
</p>
|
|
|
|
<p>
|
|
Report bugs using the
|
|
<a href="//golang.org/issue">Go issue tracker</a>.
|
|
</p>
|