什么是'。' （点或周期）在Go导入语句中做？ [英] What does the '.' (dot or period) in a Go import statement do?

问题描述

在Go教程和我看到的大部分Go代码中，软件包都是这样导入的：

 进口（
fmt
os
launchpad.net/lpad
 ... 
）
  

但在 http://bazaar.launchpad.net/~niemeyer/lpad/trunk/view/head:/session_test.go ，gocheck软件包会导入一个。

 导入（
http
。launchpad.net/ gocheck
launchpad.net/lpad
os
）
  

。（句点）的意义何在？

解决方案

如果一个明确的句点（。）出现而不是名称，所有包的导出ed标识符将在当前文件的文件块中声明，并且可以在没有限定符的情况下被访问。假设我们已经编译了一个包含package子包math的包，其中导出了函数Sin，并将编译后的软件包安装在由lib / math标识的文件中。此表说明如何在各种类型的导入声明之后导入包的文件中访问Sin。

 导入声明本地名称Sin 
 
导入lib / mathmath.Sin 
导入Mlib / mathM.Sin 
导入。 lib / mathSin 
  

Ref： http://golang.org/doc/go_spec.html#Import_declarations

In the Go tutorial, and most of the Go code I've looked at, packages are imported like this:

import (
    "fmt"
    "os"
    "launchpad.net/lpad"
    ...
)

But in http://bazaar.launchpad.net/~niemeyer/lpad/trunk/view/head:/session_test.go, the gocheck package is imported with a . (period):

import (
    "http"
    . "launchpad.net/gocheck"
    "launchpad.net/lpad"
    "os"    
)

What is the significance of the . (period)?

解决方案

It allows the identifiers in the imported package to be referred to in the local file block without a qualifier.

If an explicit period (.) appears instead of a name, all the package's exported identifiers will be declared in the current file's file block and can be accessed without a qualifier.

Assume we have compiled a package containing the package clause package math, which exports function Sin, and installed the compiled package in the file identified by "lib/math". This table illustrates how Sin may be accessed in files that import the package after the various types of import declaration.

Import declaration          Local name of Sin

import   "lib/math"         math.Sin
import M "lib/math"         M.Sin
import . "lib/math"         Sin

Ref: http://golang.org/doc/go_spec.html#Import_declarations

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