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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 泛型</title>
<link rel=stylesheet href="site.css">
</head>
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<div class="example" id="generics">
<h2><a href="./">Go by Example 中文版</a>: 泛型</h2>
<table>
<tr>
<td class="docs">
<p>从1.18版本开始，Go添加了对泛型的支持，也即类型参数。</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/t2QlBbTpgif"><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>作为泛型函数的示例，<code>MapKeys</code> 接受任意类型的Map并返回其Key的切片。
这个函数有2个类型参数 - <code>K</code> 和 <code>V</code>；
<code>K</code> 是 <code>comparable</code> 类型，也就是说我们可以通过 <code>==</code> 和 <code>!=</code>
操作符对这个类型的值进行比较。这是Go中Map的Key所必须的。
<code>V</code> 是 <code>any</code> 类型，意味着它不受任何限制 (<code>any</code> 是 <code>interface{}</code> 的别名类型).</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nx">MapKeys</span><span class="p">[</span><span class="nx">K</span> <span class="nx">comparable</span><span class="p">,</span> <span class="nx">V</span> <span class="nx">any</span><span class="p">](</span><span class="nx">m</span> <span class="kd">map</span><span class="p">[</span><span class="nx">K</span><span class="p">]</span><span class="nx">V</span><span class="p">)</span> <span class="p">[]</span><span class="nx">K</span> <span class="p">{</span>
<span class="nx">r</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="nx">K</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
<span class="k">for</span> <span class="nx">k</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">m</span> <span class="p">{</span>
<span class="nx">r</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">r</span><span class="p">,</span> <span class="nx">k</span><span class="p">)</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">r</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>作为泛型类型的示例， <code>List</code> 是一个
具有任意类型值的单链表。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">type</span> <span class="nx">List</span><span class="p">[</span><span class="nx">T</span> <span class="nx">any</span><span class="p">]</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">head</span><span class="p">,</span> <span class="nx">tail</span> <span class="o">*</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</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">type</span> <span class="nx">element</span><span class="p">[</span><span class="nx">T</span> <span class="nx">any</span><span class="p">]</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">next</span> <span class="o">*</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]</span>
<span class="nx">val</span> <span class="nx">T</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们可以像在常规类型上一样定义泛型类型的方法
但我们必须保留类型参数。
这个类型是 <code>List[T]</code>，而不是 <code>List</code></p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="p">(</span><span class="nx">lst</span> <span class="o">*</span><span class="nx">List</span><span class="p">[</span><span class="nx">T</span><span class="p">])</span> <span class="nf">Push</span><span class="p">(</span><span class="nx">v</span> <span class="nx">T</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="o">==</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">head</span> <span class="p">=</span> <span class="o">&</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]{</span><span class="nx">val</span><span class="p">:</span> <span class="nx">v</span><span class="p">}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="p">=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">head</span>
<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span><span class="p">.</span><span class="nx">next</span> <span class="p">=</span> <span class="o">&</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]{</span><span class="nx">val</span><span class="p">:</span> <span class="nx">v</span><span class="p">}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="p">=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span><span class="p">.</span><span class="nx">next</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="p">(</span><span class="nx">lst</span> <span class="o">*</span><span class="nx">List</span><span class="p">[</span><span class="nx">T</span><span class="p">])</span> <span class="nf">GetAll</span><span class="p">()</span> <span class="p">[]</span><span class="nx">T</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">elems</span> <span class="p">[]</span><span class="nx">T</span>
<span class="k">for</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">head</span><span class="p">;</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span><span class="p">;</span> <span class="nx">e</span> <span class="p">=</span> <span class="nx">e</span><span class="p">.</span><span class="nx">next</span> <span class="p">{</span>
<span class="nx">elems</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">elems</span><span class="p">,</span> <span class="nx">e</span><span class="p">.</span><span class="nx">val</span><span class="p">)</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">elems</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>
<span class="kd">var</span> <span class="nx">m</span> <span class="p">=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">int</span><span class="p">]</span><span class="kt">string</span><span class="p">{</span><span class="mi">1</span><span class="p">:</span> <span class="s">"2"</span><span class="p">,</span> <span class="mi">2</span><span class="p">:</span> <span class="s">"4"</span><span class="p">,</span> <span class="mi">4</span><span class="p">:</span> <span class="s">"8"</span><span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>当调用泛型函数的时候, 我们经常可以使用类型推断。
注意，当调用 <code>MapKeys</code> 的时候，
我们不需要为 <code>K</code> 和 <code>V</code> 指定类型 - 编译器会进行自动推断</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">"keys m:"</span><span class="p">,</span> <span class="nf">MapKeys</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>… 虽然我们也可以明确指定这些类型。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">_</span> <span class="p">=</span> <span class="nx">MapKeys</span><span class="p">[</span><span class="kt">int</span><span class="p">,</span> <span class="kt">string</span><span class="p">](</span><span class="nx">m</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"> <span class="nx">lst</span> <span class="o">:=</span> <span class="nx">List</span><span class="p">[</span><span class="kt">int</span><span class="p">]{}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">13</span><span class="p">)</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">23</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="s">"list:"</span><span class="p">,</span> <span class="nx">lst</span><span class="p">.</span><span class="nf">GetAll</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="go">keys: [4 1 2]
</span><span class="go">list: [10 13 23]</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="errors.html">错误处理</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>
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