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132 lines
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<title>std::move_only_function<R(Args...) cv ref noexcept(noex)>::operator()</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::move_only_function<R(Args...) <i>cv</i> <i>ref</i> noexcept(<i>noex</i>)>::</span>operator()</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>‎ | <a href="cpp-utility-functional-move_only_function.html">move only function</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">R operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> Args... <span class="me1">args</span> <span class="br0">)</span> <span class="coMULTI">/*cv*/</span> <span class="coMULTI">/*ref*/</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/*noex*/</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-cxx23">(C++23 起)</span></td>
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<p>以参数 <code>args</code> 调用存储的可调用对象。 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="br0">(</span><span class="br0">)</span></span></span> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*cv*/</span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ref*/</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*noex*/</span></span></span> 部分等同于 <code>std::move_only_function</code> 的模板形参的这些部分。</p>
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<p>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">invoke_r</span><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">(</span><span class="coMULTI">/*cv-ref-cast*/</span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span><span class="sy4">;</span></span></span> ，其中 <code>f</code> 是指代 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的目标对象的无 cv 限定左值，而 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*cv-ref-cast*/</span><span class="br0">(</span>f<span class="br0">)</span></span></span> 等价于：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-spar">cv</span> <span class="t-spar">ref</span> 为空或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span></span></span> ，或</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-as_const.html"><span class="kw1121">std::<span class="me2">as_const</span></span></a><span class="br0">(</span>f<span class="br0">)</span></span></span> ，若 <span class="t-spar">cv</span> <span class="t-spar">ref</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&</span></span></span> ，或</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ，若 <span class="t-spar">cv</span> <span class="t-spar">ref</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&&</span></span></span> ，或</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span><a href="cpp-utility-as_const.html"><span class="kw1121">std::<span class="me2">as_const</span></span></a><span class="br0">(</span>f<span class="br0">)</span><span class="br0">)</span></span></span> ，若 <span class="t-spar">cv</span> <span class="t-spar">ref</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&&</span></span></span> 。</li>
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</ul>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 为空则行为未定义。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>args</td>
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<td>-</td>
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<td>传递给存储的可调用目标的参数</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invoke_r</span><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">(</span><span class="coMULTI">/*cv-ref-cast*/</span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>传播底层函数调用所抛的异常。</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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<p>以下示例展示能如何按值传递 <span class="t-lc">std::move_only_function</span> 给其他函数。并且显示 <span class="t-lc">std::move_only_function</span> 能如何存储 lambda 。</p>
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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 <iostream></span>
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<span class="co2">#include <functional></span>
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<span class="kw4">void</span> call<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move_only_function</span><span class="sy1"><</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy1">></span> f<span class="br0">)</span> <span class="co1">// 能按值传递</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> f<span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> normal_function<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> <span class="nu0">42</span><span class="sy4">;</span>
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<span class="br0">}</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="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw4">auto</span> lambda <span class="sy1">=</span> <span class="br0">[</span><span class="sy3">&</span>n<span class="br0">]</span><span class="br0">(</span><span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">move_only_function</span><span class="sy1"><</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy1">></span> f <span class="sy1">=</span> lambda<span class="sy4">;</span>
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call<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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n <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span>
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call<span class="br0">(</span>lambda<span class="br0">)</span><span class="sy4">;</span>
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f <span class="sy1">=</span> normal_function<span class="sy4">;</span>
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call<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</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">1
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2
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42</pre></div>
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</div>
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</div>
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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-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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</div>
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</td>
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<td>调用其目标<br />
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<span class="t-mark">(<code>std::function<R(Args...)></code> 的公开成员函数)</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-reference_wrapper-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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</div>
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</td>
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<td>调用其所存储的函数<br />
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<span class="t-mark">(<code>std::reference_wrapper<T></code> 的公开成员函数)</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-invoke.html"><span class="t-lines"><span>invoke</span><span>invoke_r</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><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>以给定实参<span class="t-rev-inl t-since-cxx23"><span>和可能指定的返回类型</span> <span><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></span></span>调用任意<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> 对象<br />
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<span class="t-mark">(函数模板)</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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