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closures.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 闭包</title>
<link rel=stylesheet href="site.css">
</head>
<script>
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<body>
<div class="example" id="closures">
<h2><a href="./">Go by Example 中文版</a>: 闭包</h2>
<table>
<tr>
<td class="docs">
<p>Go 支持<a href="http://zh.wikipedia.org/wiki/%E5%8C%BF%E5%90%8D%E5%87%BD%E6%95%B0"><em>匿名函数</em></a>，
并能用其构造 <a href="http://zh.wikipedia.org/wiki/%E9%97%AD%E5%8C%85_(%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%A7%91%E5%AD%A6)"><em>闭包</em></a>。
匿名函数在你想定义一个不需要命名的内联函数时是很实用的。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/3qTEcKMd60U"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>intSeq</code> 函数返回一个在其函数体内定义的匿名函数。
返回的函数使用闭包的方式 <em>隐藏</em> 变量 <code>i</code>。
返回的函数 <em>隐藏</em> 变量 <code>i</code> 以形成闭包。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">intSeq</span><span class="p">()</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
<span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span>
<span class="k">return</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
<span class="nx">i</span><span class="o">++</span>
<span class="k">return</span> <span class="nx">i</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们调用 <code>intSeq</code> 函数，将返回值（一个函数）赋给 <code>nextInt</code>。
这个函数的值包含了自己的值 <code>i</code>，这样在每次调用 <code>nextInt</code> 时，都会更新 <code>i</code> 的值。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">nextInt</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>通过多次调用 <code>nextInt</code> 来看看闭包的效果。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>为了确认这个状态对于这个特定的函数是唯一的，我们重新创建并测试一下。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">newInts</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">newInts</span><span class="p">())</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="gp">$</span> go run closures.go
<span class="go">1
</span><span class="go">2
</span><span class="go">3
</span><span class="go">1</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们马上要学习关于函数的最后一个特性：递归。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="recursion.html">递归</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
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