[翻译]怎么写golang

· golang, 翻译

Introduction

This document demonstrates the development of a simple Go package and introduces the go tool, the standard way to fetch, build, and install Go packages and commands.

The go tool requires you to organize your code in a specific way. Please read this document carefully. It explains the simplest way to get up and running with your Go installation.

A similar explanation is available as a screencast.

这个文档演示了开发一个简单的Go package,介绍 go tool,标准的方法去取得(fetch),构建和安装Go package和命令.

这个go工具需要以特定的格式(way)去组织代码.请仔细阅读文档.它解释了Go安装启动和运行的最简单方法.

Code organization

Overview

Note that this differs from other programming environments in which every project has a separate workspace and workspaces are closely tied to version control repositories.

注意这和其他编程环境相比不同,在其他编程环境中,每个项目都有一个单独的工作区,并且这些工作区与版本控制存储库紧密相关.

Workspaces

A workspace is a directory hierarchy with two directories at its root:

工作空间是目录层次结构,其根目录有两个目录:

The go tool builds and installs binaries to the bin directory.

The src subdirectory typically contains multiple version control repositories (such as for Git or Mercurial) that track the development of one or more source packages.

src目录通常包含多个版本控制存储库(如Git,Mercurial),这些存储库通常追踪一个或多个source package的开发.

为了让你大致了解工作空间的外观,下面是一个示例.

To give you an idea of how a workspace looks in practice, here’s an example:

bin/
    hello                          # command executable
    outyet                         # command executable
src/
    github.com/golang/example/
        .git/                      # Git repository metadata
	hello/
	    hello.go               # command source
	outyet/
	    main.go                # command source
	    main_test.go           # test source
	stringutil/
	    reverse.go             # package source
	    reverse_test.go        # test source
    golang.org/x/image/
        .git/                      # Git repository metadata
	bmp/
	    reader.go              # package source
	    writer.go              # package source
    ... (many more repositories and packages omitted) ...

The tree above shows a workspace containing two repositories (example and image). The example repository contains two commands (hello and outyet) and one library (stringutil). The image repository contains the bmp package and several others.

A typical workspace contains many source repositories containing many packages and commands. Most Go programmers keep all their Go source code and dependencies in a single workspace.

Note that symbolic links should not be used to link files or directories into your workspace.

Commands and libraries are built from different kinds of source packages. We will discuss the distinction later.

命令和库是从不同种类的源包中构建的,稍后我们将讨论区别.

The GOPATH environment variable

The GOPATH environment variable specifies the location of your workspace. It defaults to a directory named go inside your home directory, so $HOME/go on Unix, $home/go on Plan 9, and %USERPROFILE%\go (usually C:\Users\YourName\go) on Windows.

If you would like to work in a different location, you will need to set GOPATH to the path to that directory. (Another common setup is to set GOPATH=$HOME.) Note that GOPATH must not be the same path as your Go installation.

The command go env GOPATH prints the effective current GOPATH; it prints the default location if the environment variable is unset.

go env GOPATH将会打印当前有效的GOPATH;如果没有设置环境变量,它将会打印默认位置.

For convenience, add the workspace’s bin subdirectory to your PATH:

$ export PATH=$PATH:$(go env GOPATH)/bin

The scripts in the rest of this document use $GOPATH instead of $(go env GOPATH) for brevity. To make the scripts run as written if you have not set GOPATH, you can substitute $HOME/go in those commands or else run:

为了简洁起见,本文档其余部分的脚本使用$GOPATH来代替$(go env GOPATH).要在未设置GOPATH的情况下使脚本按照编写的方式运行,可以在这些命令中替换$HOME/go或者运行:

$ export GOPATH=$(go env GOPATH)

To learn more about the GOPATH environment variable, see 'go help gopath'.

Import paths

An import path is a string that uniquely identifies a package. A package’s import path corresponds to its location inside a workspace or in a remote repository (explained below).

导入路径是一个唯一标识软件包的字符串.包的导入与其在工作区或在远处存储库的位置相对应(如下所示):

The packages from the standard library are given short import paths such as "fmt" and "net/http". For your own packages, you must choose a base path that is unlikely to collide with future additions to the standard library or other external libraries.

标准库中的软件具有简短的导入路径,例如fmtnet/http,对于我们自己的软件包,我们必须选择一个基本路径,这个基本路径不太可能与将来向标准库或其他外部库中添加的内容冲突.

If you keep your code in a source repository somewhere, then you should use the root of that source repository as your base path. For instance, if you have a GitHub account at github.com/user, that should be your base path.

如果将代码保存到源存储的某个位置,那么你应该使用该源存储库的根作为基本路径,例如,如果你有在GitHub上有一个账号,那么就应该是你的基础路径.

Note that you don’t need to publish your code to a remote repository before you can build it. It’s just a good habit to organize your code as if you will publish it someday. In practice you can choose any arbitrary path name, as long as it is unique to the standard library and greater Go ecosystem.

注意你不需要在你的代码能够运行之前把它上传到远程存储库中,这只是一个好习惯去组织你的代码,就像有一天你会发布代码一样.

We’ll use github.com/user as our base path. Create a directory inside your workspace in which to keep source code:

$ mkdir -p $GOPATH/src/github.com/user

Your first program

To compile and run a simple program, first choose a package path (we’ll use github.com/user/hello) and create a corresponding package directory inside your workspace:

$ mkdir $GOPATH/src/github.com/user/hello

为了编译并且运行一个简单的程序,首先选择一个包的路径(我们将会选择github.com/user/hello)并且创建一个相对于的包路径在你的工作区中.

Next, create a file named hello.go inside that directory, containing the following Go code.

package main

import "fmt"

func main() {
	fmt.Println("Hello, world.")
}

Now you can build and install that program with the go tool:

$ go install github.com/user/hello

Note that you can run this command from anywhere on your system. The go tool finds the source code by looking for the github.com/user/hello package inside the workspace specified by GOPATH.

You can also omit the package path if you run go install from the package directory:

$ cd $GOPATH/src/github.com/user/hello
$ go install

This command builds the hello command, producing an executable binary. It then installs that binary to the workspace’s bin directory as hello (or, under Windows, hello.exe). In our example, that will be $GOPATH/bin/hello, which is $HOME/go/bin/hello.

The go tool will only print output when an error occurs, so if these commands produce no output they have executed successfully.

You can now run the program by typing its full path at the command line:

$ $GOPATH/bin/hello
Hello, world.

Or, as you have added $GOPATH/bin to your PATH, just type the binary name:

$ hello
Hello, world.

If you’re using a source control system, now would be a good time to initialize a repository, add the files, and commit your first change. Again, this step is optional: you do not need to use source control to write Go code.

$ cd $GOPATH/src/github.com/user/hello
$ git init
Initialized empty Git repository in /home/user/go/src/github.com/user/hello/.git/
$ git add hello.go
$ git commit -m "initial commit"
[master (root-commit) 0b4507d] initial commit
 1 file changed, 7 insertion(+)
 create mode 100644 hello.go

Pushing the code to a remote repository is left as an exercise for the reader.

Your first library

Let’s write a library and use it from the hello program.

Again, the first step is to choose a package path (we’ll use github.com/user/stringutil) and create the package directory:

$ mkdir $GOPATH/src/github.com/user/stringutil

Next, create a file named reverse.go in that directory with the following contents.

// Package stringutil contains utility functions for working with strings.
package stringutil

// Reverse returns its argument string reversed rune-wise left to right.
func Reverse(s string) string {
	r := []rune(s)
	for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
		r[i], r[j] = r[j], r[i]
	}
	return string(r)
}

Now, test that the package compiles with go build:

$ go build github.com/user/stringutil

Or, if you are working in the package’s source directory, just:

$ go build

This won’t produce an output file. Instead it saves the compiled package in the local build cache.

After confirming that the stringutil package builds, modify your original hello.go (which is in $GOPATH/src/github.com/user/hello) to use it:

package main

import (
	"fmt"

	"github.com/user/stringutil"
)

func main() {
	fmt.Println(stringutil.Reverse("!oG ,olleH"))
}

Install the hello program:

$ go install github.com/user/hello

Running the new version of the program, you should see a new, reversed message:

$ hello
Hello, Go!

After the steps above, your workspace should look like this:

bin/
    hello                 # command executable
src/
    github.com/user/
        hello/
            hello.go      # command source
        stringutil/
            reverse.go    # package source

Package names

The first statement in a Go source file must be

package name

where name is the package’s default name for imports. (All files in a package must use the same name.)

Go’s convention is that the package name is the last element of the import path: the package imported as “crypto/rot13” should be named rot13.

Go的约定是包的名字是导入目录的最后一个元素:如”crypto/rot13”包的名字应该是rot13

Executable commands must always use package main.

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.

See Effective Go to learn more about Go’s naming conventions.

Testing

Go has a lightweight test framework composed of the go test command and the testing package.

Go有一个轻量级测试框架由go testtesting包组成.

You write a test by creating a file with a name ending in _test.go that contains functions named TestXXX with signature func (t *testing.T). The test framework runs each such function; if the function calls a failure function such as t.Error or t.Fail, the test is considered to have failed.

通过创建一个名称以_test.go结尾的文件来编写测试,该文件包含名为TestXXX且具有签名func (t *testing.T)的函数. 测试框架运行每个这样的功能.如果该函数调用诸如t.Errort.Fail的失败函数,则认为测试已失败.

Add a test to the stringutil package by creating the file $GOPATH/src/github.com/user/stringutil/reverse_test.go containing the following Go code.

package stringutil

import "testing"

func TestReverse(t *testing.T) {
	cases := []struct {
		in, want string
	}{
		{"Hello, world", "dlrow ,olleH"},
		{"Hello, 世界", "界世 ,olleH"},
		{"", ""},
	}
	for _, c := range cases {
		got := Reverse(c.in)
		if got != c.want {
			t.Errorf("Reverse(%q) == %q, want %q", c.in, got, c.want)
		}
	}
}

Then run the test with go test:

$ go test github.com/user/stringutil
ok  	github.com/user/stringutil 0.165s

As always, if you are running the go tool from the package directory, you can omit the package path:

$ go test
ok  	github.com/user/stringutil 0.165s

Run go help test and see the testing package documentation for more detail.

Remote packages

An import path can describe how to obtain the package source code using a revision control system such as Git or Mercurial. The go 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 github.com/golang/example. If you include the repository URL in the package’s import path, go get will fetch, build, and install it automatically:

$ go get github.com/golang/example/hello
$ $GOPATH/bin/hello
Hello, Go examples!

导入路径可以描述如何使用修订控制系统(例如Git或者Mercurial)获取软件包源代码.go工具使用此属性来自动从远程存储库获取软件包.例如,本文档描述的示例也保存在GitHub托管的Git存储库中.如果你在软件包的导入路径包含存储库URL,则go get将会自动获取,构建和安装它.

If the specified package is not present in a workspace, go get will place it inside the first workspace specified by GOPATH. (If the package does already exist, go get skips the remote fetch and behaves the same as go install.)

After issuing the above go get command, the workspace directory tree should now look like this:

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

The hello command hosted at GitHub depends on the stringutil package within the same repository. The imports in hello.go file use the same import path convention, so the go get command is able to locate and install the dependent package, too.

import "github.com/golang/example/stringutil"

This convention is the easiest way to make your Go packages available for others to use. The Go Wiki and godoc.org provide lists of external Go projects.

For more information on using remote repositories with the go tool, see go help importpath.

What’s next

Subscribe to the golang-announce mailing list to be notified when a new stable version of Go is released.

See Effective Go for tips on writing clear, idiomatic Go code.

看Effective Go来获取编写清晰惯用的Go代码的提示.

Take A Tour of Go to learn the language proper.

通过A Tour of Go来正确的学习.

Visit the documentation page for a set of in-depth articles about the Go language and its libraries and tools.

访问文档页面,来获取有关Go语言以及库和工具的一系列深入文章.

Getting help

For real-time help, ask the helpful gophers in #go-nuts on the Freenode IRC server.

The official mailing list for discussion of the Go language is Go Nuts.

Report bugs using the Go issue tracker.

翻译网页:https://golang.org/doc/code.html