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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: Embedding</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'interfaces';
}
if (e.key == "ArrowRight") {
window.location.href = 'generics';
}
}
</script>
<body>
<div class="example" id="embedding">
<h2><a href="./">Go by Example 中文版</a>: Embedding</h2>
<table>
<tr>
<td class="docs">
<p>Go支持对于结构体(struct)和接口(interfaces)的 <em>嵌入(embedding)</em>
以表达一种更加无缝的 <em>组合(composition)</em> 类型</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/H7Y5_WdmyMW"><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">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">type</span> <span class="nx">base</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">num</span> <span class="kt">int</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="p">(</span><span class="nx">b</span> <span class="nx">base</span><span class="p">)</span> <span class="nf">describe</span><span class="p">()</span> <span class="kt">string</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Sprintf</span><span class="p">(</span><span class="s">"base with num=%v"</span><span class="p">,</span> <span class="nx">b</span><span class="p">.</span><span class="nx">num</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>一个 <code>container</code> <em>嵌入</em> 了一个 <code>base</code>.
一个嵌入看起来像一个没有名字的字段</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">type</span> <span class="nx">container</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">base</span>
<span class="nx">str</span> <span class="kt">string</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>当创建含有嵌入的结构体，必须对嵌入进行显式的初始化；
在这里使用嵌入的类型当作字段的名字</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">co</span> <span class="o">:=</span> <span class="nx">container</span><span class="p">{</span>
<span class="nx">base</span><span class="p">:</span> <span class="nx">base</span><span class="p">{</span>
<span class="nx">num</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span>
<span class="p">},</span>
<span class="nx">str</span><span class="p">:</span> <span class="s">"some name"</span><span class="p">,</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们可以直接在 <code>co</code> 上访问 base 中定义的字段,
例如： <code>co.num</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"co={num: %v, str: %v}\n"</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">num</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">str</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>或者，我们可以使用嵌入的类型名拼写出完整的路径。</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="s">"also num:"</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">base</span><span class="p">.</span><span class="nx">num</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>由于 <code>container</code> 嵌入了 <code>base</code>，因此<code>base</code>的方法
也成为了 <code>container</code> 的方法。在这里我们直接在 <code>co</code> 上
调用了一个从 <code>base</code> 嵌入的方法。</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="s">"describe:"</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nf">describe</span><span class="p">())</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="kd">type</span> <span class="nx">describer</span> <span class="kd">interface</span> <span class="p">{</span>
<span class="nf">describe</span><span class="p">()</span> <span class="kt">string</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>可以使用带有方法的嵌入结构来赋予接口实现到其他结构上。
因为嵌入了 <code>base</code> ，在这里我们看到 <code>container</code>
也实现了 <code>describer</code> 接口。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="kd">var</span> <span class="nx">d</span> <span class="nx">describer</span> <span class="p">=</span> <span class="nx">co</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"describer:"</span><span class="p">,</span> <span class="nx">d</span><span class="p">.</span><span class="nf">describe</span><span class="p">())</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run embedding.go
<span class="go">co={num: 1, str: some name}
</span><span class="go">also num: 1
</span><span class="go">describe: base with num=1
</span><span class="go">describer: base with num=1</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="generics">泛型</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>
<script>
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('type base struct {\u000A num int\u000A}\u000A');codeLines.push('func (b base) describe() string {\u000A return fmt.Sprintf(\"base with num\u003D%v\", b.num)\u000A}\u000A');codeLines.push('type container struct {\u000A base\u000A str string\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' co :\u003D container{\u000A base: base{\u000A num: 1,\u000A },\u000A str: \"some name\",\u000A }\u000A');codeLines.push(' fmt.Printf(\"co\u003D{num: %v, str: %v}\\n\", co.num, co.str)\u000A');codeLines.push(' fmt.Println(\"also num:\", co.base.num)\u000A');codeLines.push(' fmt.Println(\"describe:\", co.describe())\u000A');codeLines.push(' type describer interface {\u000A describe() string\u000A }\u000A');codeLines.push(' var d describer \u003D co\u000A fmt.Println(\"describer:\", d.describe())\u000A}\u000A');codeLines.push('');
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</body>
</html>