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<title>std::variant<Types...>::~variant</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_variant_variant skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::variant<Types...>::</span>~variant</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-variant.html">variant</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<div><span class="mw-geshi cpp source-cpp">~variant<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> ~variant<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>若 <a href="cpp-utility-variant-valueless_by_exception.html"><code>valueless_by_exception()</code></a> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则不做任何事。否则销毁当前所含值。</p>
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<p>若对于所有 <code>Types...</code> 中的 <code>T_i</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_destructible.html"><span class="kw565">std::<span class="me2">is_trivially_destructible_v</span></span></a><span class="sy1"><</span>T_i<span class="sy1">></span></span></span> 为 <code>true</code> ，则此析构函数为平凡。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <variant></span>
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<span class="co2">#include <cstdio></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">struct</span> X <span class="br0">{</span> ~X<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> puts<span class="br0">(</span><span class="st0">"X::~X();"</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">struct</span> Y <span class="br0">{</span> ~Y<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> puts<span class="br0">(</span><span class="st0">"Y::~Y();"</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="br0">{</span>
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puts<span class="br0">(</span><span class="st0">"entering block #1"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>X,Y<span class="sy1">></span> var<span class="sy4">;</span>
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puts<span class="br0">(</span><span class="st0">"leaving block #1"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">{</span>
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puts<span class="br0">(</span><span class="st0">"entering block #2"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1"><</span>X,Y<span class="sy1">></span> var<span class="br0">{</span> <a href="cpp-utility-in_place.html"><span class="kw1084">std::<span class="me2">in_place_index_t</span></span></a><span class="sy1"><</span><span class="nu0">1</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// constructs var(Y)</span>
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puts<span class="br0">(</span><span class="st0">"leaving block #2"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">entering block #1
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leaving block #1
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X::~X();
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entering block #2
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leaving block #2
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Y::~Y();</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2231R1">P2231R1</a></td>
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<td>C++20</td>
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<td>析构函数不是 constexpr ，而非平凡析构函数在 C++20 中能为 constexpr</td>
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<td>使之为 constexpr</td>
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</tr>
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</table>
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<div class="visualClear"></div>
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