207 lines
19 KiB
HTML
207 lines
19 KiB
HTML
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<title>std::move_only_function</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_move_only_function 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::</span>move_only_function</h1>
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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-functional.html">functional</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-functional.html"><functional></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span>... <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy4">;</span> <span class="co1">// 不定义</span></span></div>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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<tr class="t-dcl t-since-cxx23">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br /></span>
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<p><span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="sy3">&</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="sy3">&&</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="sy3">&&</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span> <span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span> <span class="sy3">&</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span> <span class="sy3">&&</span><span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br /></p>
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<span class="kw1">class</span> move_only_function<span class="sy1"><</span>R<span class="br0">(</span>Args...<span class="br0">)</span> <span class="kw4">const</span> <span class="sy3">&&</span> <span class="kw1">noexcept</span><span class="sy1">></span><span class="sy4">;</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-cxx23">(C++23 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<p>类模板 <code>std::move_only_function</code> 是通用的多态函数包装。 <code>std::move_only_function</code> 对象存储并调用任何可构造（不要求为可移动构造）的<a href="cpp-named_req-Callable.html"><span style="font-style:italic">可调用</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Callable)</span></a> <i>目标</i>——函数、 <a href="cpp-language-lambda.html">lambda 表达式</a>、 <a href="cpp-utility-functional-bind.html">bind 表达式</a>或其他函数对象，以及成员函数指针和成员对象指针。</p>
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<p>称存储的可调用对象为 <code>std::move_only_function</code> 的<i>目标</i>。若 <code>std::move_only_function</code> 不含目标，则称之为<i>空</i>。不同于 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> ，调用<i>空</i>的 <code>std::move_only_function</code> 导致未定义行为。</p>
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<p><code>std::move_only_functions</code> 支持在其模板形参中提供的不含 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">volatile</span></span></span> 的每种 <a href="cpp-language-member_functions.html#.E6.9C.89_const_.E4.B8.8E_volatile_.E9.99.90.E5.AE.9A.E7.9A.84.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">cv 限定符</a>、<a href="cpp-language-member_functions.html#.E6.9C.89.E5.BC.95.E7.94.A8.E9.99.90.E5.AE.9A.E7.9A.84.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">引用限定符</a>及 <a href="cpp-language-noexcept_spec.html">noexcept 说明符</a>的组合。这些限定符与说明符（若存在）被添加到其 <a href="cpp-utility-functional-move_only_function-operator().html"><code>operator()</code></a> 。</p>
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<p><code>std::move_only_function</code> 满足<a href="cpp-named_req-MoveConstructible.html"><span style="font-style:italic">可移动构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveConstructible)</span></a> 与<a href="cpp-named_req-MoveAssignable.html"><span style="font-style:italic">可移动赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveAssignable)</span></a> 的要求，但不满足<a href="cpp-named_req-CopyConstructible.html"><span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span></a> 或<a href="cpp-named_req-CopyAssignable.html"><span style="font-style:italic">可复制赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyAssignable)</span></a> 。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>类型</td>
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<td>定义</td>
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<tr class="t-dsc">
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<td><code>result_type</code></td>
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<td><code>R</code></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-utility-functional-move_only_function-move_only_function.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>构造新的 <code>std::move_only_function</code> 对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-utility-functional-move_only_function-~move_only_function.html"><span class="t-lines"><span>(析构函数)</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>销毁 <code>std::move_only_function</code> 对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-operator=.html"><span class="t-lines"><span>operator=</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>替换或销毁目标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>交换二个 <code>std::move_only_function</code> 对象的目标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-operator_bool.html"><span class="t-lines"><span>operator bool</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>检查 <code>std::move_only_function</code> 是否拥有目标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>调用目标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-swap2.html"><span class="t-lines"><span>swap<span class="t-dsc-small">(std::move_only_function)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>重载 <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span> 算法<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-operator==.html"><span class="t-lines"><span>operator==</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>比较 <code>std::move_only_function</code> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span><br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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</table>
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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>推荐实现存储有较小大小的可调用对象于 <code>std::move_only_function</code> 对象内部。这种小对象优化等效地对于函数指针和 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 特化要求，并且只能应用到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_move_constructible.html"><span class="kw543">std::<span class="me2">is_nothrow_move_constructible_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的类型 <code>T</code> 。</p>
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<p>类似 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> ，若 <code>R</code> 为能绑定到右值的引用类型，则 <code>std::move_only_function</code> 可能包装按值返回的函数对象，该情况下对这种 <code>std::move_only_function</code> 的调用始终返回悬垂引用。</p>
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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">std<span class="sy4">::</span><span class="me2">move_only_function</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">int</span><span class="sy3">&</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy1">></span> uf<span class="br0">(</span><span class="br0">[</span><span class="br0">]</span><span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">42</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> x <span class="sy1">=</span> uf<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 未定义行为： uf() 的结果为悬垂引用</span></pre></div>
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</div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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</tr>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-function.html"><span class="t-lines"><span>function</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>包装具有指定函数调用签名的任意可复制构造类型的可调用对象<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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