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类型断言 # // 方式1 var ( v T ok bool ) v, ok = x.(T) // 方式2 v, ok := x.(T) // x是接口类型的变量，T是要断言的类型 // 方式3 var v, ok = x.(T) // 方式4 v := x.(T) // 当心此种方式断言，若断言失败会发生恐慌 判断key是否存在映射中 # // 方式1 v, ok := a[x] // 方式2 var v, ok = a[x] 判断通道是否关闭 # // 方式1 var ( x T ok bool ) x, ok = &lt;-ch // 方式2 x, ok := &lt;-ch // 方式3 var x, ok = &lt;-ch ">
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<meta property="og:description" content=" 逗号ok模式 # 通过逗号ok模式(comma ok idiom)，我们可以进行类型断言，判断映射中是否存在某个key以及通道是否关闭。
类型断言 # // 方式1 var ( v T ok bool ) v, ok = x.(T) // 方式2 v, ok := x.(T) // x是接口类型的变量，T是要断言的类型 // 方式3 var v, ok = x.(T) // 方式4 v := x.(T) // 当心此种方式断言，若断言失败会发生恐慌 判断key是否存在映射中 # // 方式1 v, ok := a[x] // 方式2 var v, ok = a[x] 判断通道是否关闭 # // 方式1 var ( x T ok bool ) x, ok = &lt;-ch // 方式2 x, ok := &lt;-ch // 方式3 var x, ok = &lt;-ch " />
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<strong>逗号ok模式</strong>
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<article class="markdown"><h1 id="逗号ok模式">
逗号ok模式
<a class="anchor" href="#%e9%80%97%e5%8f%b7ok%e6%a8%a1%e5%bc%8f">#</a>
</h1>
<p>通过逗号ok模式(comma ok idiom)，我们可以进行类型断言，判断映射中是否存在某个key以及通道是否关闭。</p>
<h2 id="类型断言">
类型断言
<a class="anchor" href="#%e7%b1%bb%e5%9e%8b%e6%96%ad%e8%a8%80">#</a>
</h2>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span><span style="color:#75715e">// 方式1
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#66d9ef">var</span> (
</span></span><span style="display:flex;"><span> <span style="color:#a6e22e">v</span> <span style="color:#a6e22e">T</span>
</span></span><span style="display:flex;"><span> <span style="color:#a6e22e">ok</span> <span style="color:#66d9ef">bool</span>
</span></span><span style="display:flex;"><span>)
</span></span><span style="display:flex;"><span><span style="color:#a6e22e">v</span>, <span style="color:#a6e22e">ok</span> = <span style="color:#a6e22e">x</span>.(<span style="color:#a6e22e">T</span>)
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式2
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#a6e22e">v</span>, <span style="color:#a6e22e">ok</span> <span style="color:#f92672">:=</span> <span style="color:#a6e22e">x</span>.(<span style="color:#a6e22e">T</span>) <span style="color:#75715e">// x是接口类型的变量，T是要断言的类型
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式3
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#66d9ef">var</span> <span style="color:#a6e22e">v</span>, <span style="color:#a6e22e">ok</span> = <span style="color:#a6e22e">x</span>.(<span style="color:#a6e22e">T</span>)
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式4
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#a6e22e">v</span> <span style="color:#f92672">:=</span> <span style="color:#a6e22e">x</span>.(<span style="color:#a6e22e">T</span>) <span style="color:#75715e">// 当心此种方式断言，若断言失败会发生恐慌
</span></span></span></code></pre></div><h2 id="判断key是否存在映射中">
判断key是否存在映射中
<a class="anchor" href="#%e5%88%a4%e6%96%adkey%e6%98%af%e5%90%a6%e5%ad%98%e5%9c%a8%e6%98%a0%e5%b0%84%e4%b8%ad">#</a>
</h2>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span><span style="color:#75715e">// 方式1
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#a6e22e">v</span>, <span style="color:#a6e22e">ok</span> <span style="color:#f92672">:=</span> <span style="color:#a6e22e">a</span>[<span style="color:#a6e22e">x</span>]
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式2
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#66d9ef">var</span> <span style="color:#a6e22e">v</span>, <span style="color:#a6e22e">ok</span> = <span style="color:#a6e22e">a</span>[<span style="color:#a6e22e">x</span>]
</span></span></code></pre></div><h2 id="判断通道是否关闭">
判断通道是否关闭
<a class="anchor" href="#%e5%88%a4%e6%96%ad%e9%80%9a%e9%81%93%e6%98%af%e5%90%a6%e5%85%b3%e9%97%ad">#</a>
</h2>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-go" data-lang="go"><span style="display:flex;"><span><span style="color:#75715e">// 方式1
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#66d9ef">var</span> (
</span></span><span style="display:flex;"><span> <span style="color:#a6e22e">x</span> <span style="color:#a6e22e">T</span>
</span></span><span style="display:flex;"><span> <span style="color:#a6e22e">ok</span> <span style="color:#66d9ef">bool</span>
</span></span><span style="display:flex;"><span>)
</span></span><span style="display:flex;"><span><span style="color:#a6e22e">x</span>, <span style="color:#a6e22e">ok</span> = <span style="color:#f92672">&lt;-</span><span style="color:#a6e22e">ch</span>
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式2
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#a6e22e">x</span>, <span style="color:#a6e22e">ok</span> <span style="color:#f92672">:=</span> <span style="color:#f92672">&lt;-</span><span style="color:#a6e22e">ch</span>
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#75715e">// 方式3
</span></span></span><span style="display:flex;"><span><span style="color:#75715e"></span><span style="color:#66d9ef">var</span> <span style="color:#a6e22e">x</span>, <span style="color:#a6e22e">ok</span> = <span style="color:#f92672">&lt;-</span><span style="color:#a6e22e">ch</span>
</span></span></code></pre></div></article>
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