70 lines
4.1 KiB
HTML
70 lines
4.1 KiB
HTML
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>std::optional<T>::~optional</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_optional_optional skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::optional<T>::</span>~optional</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-optional.html">optional</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">~optional<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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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> ~optional<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>若对象含值且类型 <code>T</code> 非可平凡析构（见 <span class="t-lc"><a href="cpp-types-is_destructible.html">std::is_trivially_destructible</a></span> ），则如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">value<span class="br0">(</span><span class="br0">)</span>.<span class="me1">T</span><span class="sy4">::</span>~T<span class="br0">(</span><span class="br0">)</span></span></span> 一般，通过调用其析构函数销毁所含值。</p>
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<p>否则，不做任何事。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>若 <code>T</code> 为可平凡析构，则此析构函数亦为平凡，故 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span> 亦为可平凡析构。</p>
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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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<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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<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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