226 lines
20 KiB
HTML
226 lines
20 KiB
HTML
<!DOCTYPE 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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<title>std::function<R(Args...)>::function</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_function_function 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::function<R(Args...)>::</span>function</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-functional.html">functional</a>‎ | <a href="cpp-utility-functional-function.html">function</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">function<span class="br0">(</span><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>(1)</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 t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp">function<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>
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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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</tr>
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<tr class="t-dcl t-since-cxx11">
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<td>
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<div><span class="mw-geshi cpp source-cpp">function<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>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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</tbody>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<tr class="t-dcl-rev-aux">
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<td></td>
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<td rowspan="142">(4)</td>
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<td></td>
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<tr class="t-dcl t-since-cxx11 t-until-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp">function<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>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp">function<span class="br0">(</span> function<span class="sy3">&&</span> other <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 class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tbody>
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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="br0">(</span> F<span class="sy3">&&</span> f <span class="br0">)</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>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<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> Alloc <span class="sy1">></span><br />
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function<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Alloc<span class="sy3">&</span> alloc <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>(6)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<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> Alloc <span class="sy1">></span><br /></span>
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<p>function<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Alloc<span class="sy3">&</span> alloc,<br /></p>
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<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></div>
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</td>
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<td>(7)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<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> Alloc <span class="sy1">></span><br /></span>
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<p>function<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Alloc<span class="sy3">&</span> alloc,<br /></p>
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<span class="kw4">const</span> function<span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(8)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<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> Alloc <span class="sy1">></span><br /></span>
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<p>function<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Alloc<span class="sy3">&</span> alloc,<br /></p>
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function<span class="sy3">&&</span> other <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(9)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11 t-until-cxx17">
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<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="kw1">class</span> Alloc <span class="sy1">></span><br />
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function<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Alloc<span class="sy3">&</span> alloc, F f <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(10)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</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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<td></td>
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</tr>
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</tbody>
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</table>
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<p>从各种资源构造 <code>std::function</code> 。</p>
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<div class="t-li1"><span class="t-li">1-2)</span> 构造<i>空</i> <code>function</code> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 复制 <span class="t-v">(3)</span> 或移动 <span class="t-v">(4)</span> <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> 的<i>目标</i>。若 <code>other</code> 为<i>空</i>，则调用后 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 将亦为<i>空</i>。对于 <span class="t-v">(4)</span> ， <code>other</code> 在调用后处于合法但未指定的状态。</div>
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<div class="t-li1"><span class="t-li">5)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><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></span> 初始化<i>目标</i>。<i>目标</i>的类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 。若 <code>f</code> 是空指针、指向成员的空指针或某 <code>std::function</code> 特化的空值，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 在此调用后将为<i>空</i>。此构造函数不参与重载决议，除非目标类型与 <code>function</code> 不相同，且其左值对参数类型 <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> 。若目标类型不可复制构造或目标的初始化非良构，则程序非良构。</div>
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<div class="t-li1"><span class="t-li">6-10)</span> 同 <span class="t-v">(1-5)</span> ，除了将 <code>alloc</code> 用于分配任何 <code>function</code> 会用到的内部数据结构的内存。</div>
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<p><i>目标</i>是函数指针或 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 时，保证使用小对象优化，即始终直接存储这些目标于 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 对象中，不发生动态内存分配。可以构造其他大对象于动态分配的存储中，并由 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 对象通过指针访问。</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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<tr class="t-par">
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<td>other</td>
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<td>-</td>
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<td>用于初始化 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的函数对象</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>用于初始化 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的可调用对象</td>
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</tr>
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<tr class="t-par">
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<td>alloc</td>
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<td>-</td>
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<td>用于内部内存分配的<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a></td>
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</tr>
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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>
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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><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span></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> 和 <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> 的要求。</td>
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</tr>
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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>Alloc</code> 必须满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 的要求。</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">3,8,9)</span> 若 <code>other</code> 的<i>目标</i>是函数指针或 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 则不抛出异常，否则可能抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 或用于复制或移动存储的可调用对象的构造函数所抛的异常。</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx20">
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<td>
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<div class="t-li1"><span class="t-li">4)</span> 若 <code>other</code> 的<i>目标</i>是函数指针或 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 则不抛出异常，否则可能抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 或用于复制或移动存储的可调用对象的构造函数所抛的异常。</div>
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</td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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</table>
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<div class="t-li1"><span class="t-li">5,10)</span> 若 <code>f</code> 是函数指针或 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 则不抛异常，否则可能抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 或存储的可调用对象的复制构造函数所抛的异常。</div>
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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><code>std::function</code> 的分配器支持说明贫乏，且实现不一致。一些实现完全不提供重载 <span class="t-v">(6-10)</span> ，一些提供重载但忽略提供的分配器参数，而一些实现提供重载并将提供的分配器用于构造，但不在重赋值 <code>std::function</code> 时使用。结果， C++17 中移除了分配器支持。</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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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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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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</table>
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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> 对象的构造函数可能有歧义</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/issue2774">LWG 2774</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> 对象的函数进行一次额外移动</td>
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<td>已消除</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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<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>(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">(<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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</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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