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<li><em>Go语言圣经读书笔记(挖坑中...): <a href="https://github.com/chai2010/gopl-notes-zh">https://github.com/chai2010/gopl-notes-zh</a></em></li>
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<hr>
<h2 id="18-本章要点"><a class="header" href="#18-本章要点">1.8. 本章要点</a></h2>
<p>本章对Go语言做了一些介绍，Go语言很多方面在有限的篇幅中无法覆盖到。本节会把没有讲到的内容也做一些简单的介绍，这样读者在读到完整的内容之前，可以有个简单的印象。</p>
<p><strong>控制流：</strong> 在本章我们只介绍了if控制和for，但是没有提到switch多路选择。这里是一个简单的switch的例子：</p>
<pre><code class="language-go">switch coinflip() {
case &quot;heads&quot;:
heads++
case &quot;tails&quot;:
tails++
default:
fmt.Println(&quot;landed on edge!&quot;)
}
</code></pre>
<p>在翻转硬币的时候，例子里的coinflip函数返回几种不同的结果，每一个case都会对应一个返回结果，这里需要注意，Go语言并不需要显式地在每一个case后写break，语言默认执行完case后的逻辑语句会自动退出。当然了，如果你想要相邻的几个case都执行同一逻辑的话，需要自己显式地写上一个fallthrough语句来覆盖这种默认行为。不过fallthrough语句在一般的程序中很少用到。</p>
<p>Go语言里的switch还可以不带操作对象（译注：switch不带操作对象时默认用true值代替，然后将每个case的表达式和true值进行比较）；可以直接罗列多种条件，像其它语言里面的多个if else一样，下面是一个例子：</p>
<pre><code class="language-go">func Signum(x int) int {
switch {
case x &gt; 0:
return +1
default:
return 0
case x &lt; 0:
return -1
}
}
</code></pre>
<p>这种形式叫做无tag switch(tagless switch)；这和switch true是等价的。</p>
<p>像for和if控制语句一样，switch也可以紧跟一个简短的变量声明，一个自增表达式、赋值语句，或者一个函数调用（译注：比其它语言丰富）。</p>
<p>break和continue语句会改变控制流。和其它语言中的break和continue一样，break会中断当前的循环，并开始执行循环之后的内容，而continue会跳过当前循环，并开始执行下一次循环。这两个语句除了可以控制for循环，还可以用来控制switch和select语句（之后会讲到），在1.3节中我们看到，continue会跳过内层的循环，如果我们想跳过的是更外层的循环的话，我们可以在相应的位置加上label，这样break和continue就可以根据我们的想法来continue和break任意循环。这看起来甚至有点像goto语句的作用了。当然，一般程序员也不会用到这种操作。这两种行为更多地被用到机器生成的代码中。</p>
<p><strong>命名类型：</strong> 类型声明使得我们可以很方便地给一个特殊类型一个名字。因为struct类型声明通常非常地长，所以我们总要给这种struct取一个名字。本章中就有这样一个例子，二维点类型：</p>
<pre><code class="language-go">type Point struct {
X, Y int
}
var p Point
</code></pre>
<p>类型声明和命名类型会在第二章中介绍。</p>
<p><strong>指针：</strong> Go语言提供了指针。指针是一种直接存储了变量的内存地址的数据类型。在其它语言中，比如C语言，指针操作是完全不受约束的。在另外一些语言中，指针一般被处理为“引用”，除了到处传递这些指针之外，并不能对这些指针做太多事情。Go语言在这两种范围中取了一种平衡。指针是可见的内存地址，&amp;操作符可以返回一个变量的内存地址，并且*操作符可以获取指针指向的变量内容，但是在Go语言里没有指针运算，也就是不能像c语言里可以对指针进行加或减操作。我们会在2.3.2中进行详细介绍。</p>
<p><strong>方法和接口：</strong> 方法是和命名类型关联的一类函数。Go语言里比较特殊的是方法可以被关联到任意一种命名类型。在第六章我们会详细地讲方法。接口是一种抽象类型，这种类型可以让我们以同样的方式来处理不同的固有类型，不用关心它们的具体实现，而只需要关注它们提供的方法。第七章中会详细说明这些内容。</p>
<p><strong>包（packages）：</strong> Go语言提供了一些很好用的package，并且这些package是可以扩展的。Go语言社区已经创造并且分享了很多很多。所以Go语言编程大多数情况下就是用已有的package来写我们自己的代码。通过这本书，我们会讲解一些重要的标准库内的package，但是还是有很多限于篇幅没有去说明，因为我们没法在这样的厚度的书里去做一部代码大全。</p>
<p>在你开始写一个新程序之前，最好先去检查一下是不是已经有了现成的库可以帮助你更高效地完成这件事情。你可以在 https://golang.org/pkg 和 https://godoc.org 中找到标准库和社区写的package。godoc这个工具可以让你直接在本地命令行阅读标准库的文档。比如下面这个例子。</p>
<pre><code>$ go doc http.ListenAndServe
package http // import &quot;net/http&quot;
func ListenAndServe(addr string, handler Handler) error
ListenAndServe listens on the TCP network address addr and then
calls Serve with handler to handle requests on incoming connections.
...
</code></pre>
<p><strong>注释：</strong> 我们之前已经提到过了在源文件的开头写的注释是这个源文件的文档。在每一个函数之前写一个说明函数行为的注释也是一个好习惯。这些惯例很重要，因为这些内容会被像godoc这样的工具检测到，并且在执行命令时显示这些注释。具体可以参考10.7.4。</p>
<p>多行注释可以用 <code>/* ... */</code> 来包裹，和其它大多数语言一样。在文件一开头的注释一般都是这种形式，或者一大段的解释性的注释文字也会被这符号包住，来避免每一行都需要加//。在注释中//和/*是没什么意义的，所以不要在注释中再嵌入注释。</p>
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