150 lines
11 KiB
HTML
150 lines
11 KiB
HTML
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<title>std::function<R(Args...)>::operator=</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_function_operator 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::function<R(Args...)>::</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-function.html">function</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">function<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> function<span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">function<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> function<span class="sy3">&&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">function<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-types-nullptr_t.html"><span class="kw102">std::<span class="me2">nullptr_t</span></span></a> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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> F <span class="sy1">></span><br />
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function<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> F<span class="sy3">&&</span> f <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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> F <span class="sy1">></span><br />
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function<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-utility-functional-reference_wrapper.html"><span class="kw1068">std::<span class="me2">reference_wrapper</span></span></a><span class="sy1"><</span>F<span class="sy1">></span> f <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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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<td></td>
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<p>赋值新<i>目标</i>给 <code>std::function</code> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 赋值 <code>other</code> 的<i>目标</i>副本，如同以执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">function<span class="br0">(</span>other<span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span></div>
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<div class="t-li1"><span class="t-li">2)</span> 移动 <code>other</code> 的<i>目标</i>到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 。 <code>other</code> 在有未指定值的合法状态。</div>
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<div class="t-li1"><span class="t-li">3)</span> 舍弃当前<i>目标</i>。 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 在调用后为<i>空</i>。</div>
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<div class="t-li1"><span class="t-li">4)</span> 设置 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的<i>目标</i>为可调用的 <code>f</code> ，如同以执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">function<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>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span><span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span> 。此运算符不参与重载决议，除非 <code>f</code> 对于参数类型 <code>Args...</code> 和返回类型 <code>R</code> <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> 。</div>
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<div class="t-li1"><span class="t-li">5)</span> 设置 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的<i>目标</i>为 <code>f</code> 的副本，如同以执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">function<span class="br0">(</span>f<span class="br0">)</span>.<span class="me1">swap</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="sy4">;</span></span></span></div>
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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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<tr class="t-par">
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<td>other</td>
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<td>-</td>
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<td>要复制其目标的另一 <code>std::function</code> 对象</td>
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</tr>
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<tr class="t-par">
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<td>f</td>
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<td>-</td>
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<td>用以初始化<i>目标</i>的可调用对象</td>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>F</code> 必须满足<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> 的要求。</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"><span class="sy2">*</span>this</span></span></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>虽然 C++17 中从 <code>std::function</code> 移除了以前的分配器支持，这些赋值运算符使用默认分配器，而不是 <code>*this</code> 或 <code>other</code> 的分配器（见 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2386">LWG 问题 2386</a> ）。</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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<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://cplusplus.github.io/LWG/issue2132">LWG 2132</a></td>
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<td>C++11</td>
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<td>接收一个<span style="font-style:italic">可调用</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Callable)</span> 对象的重载可能有歧义</td>
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<td>已约束</td>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2401">LWG 2401</a></td>
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<td>C++11</td>
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<td>未要求源自 <code>std::nullptr_t</code> 的构造函数为 noexcept</td>
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<td>已要求</td>
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</tr>
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</table>
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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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<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">(<code>std::move_only_function<R(Args...) <i>cv</i> <i>ref</i> noexcept(<i>noex</i>)></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-function-assign.html"><span class="t-lines"><span>assign</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></span></span></div>
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</div>
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</td>
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<td>为内容赋值一个新的目标<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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</table>
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<table class="t-dsc-begin">
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<td></td>
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</div>
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<div class="visualClear"></div>
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