117 lines
7.0 KiB
HTML
117 lines
7.0 KiB
HTML
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<title>std::uses_allocator<std::function></title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_function_uses_allocator 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>uses_allocator<small><std::function></small></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>定义于头文件 <code><a href="cpp-header-functional.html"><functional></a></code></div>
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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">ArgTypes</span>, <span class="kw1">class</span> Alloc <span class="sy1">></span><br />
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<span class="kw1">struct</span> uses_allocator<span class="sy1"><</span><a href="cpp-utility-functional-function.html"><span class="kw1059">std::<span class="me2">function</span></span></a><span class="sy1"><</span>R<span class="br0">(</span>ArgTypes...<span class="br0">)</span><span class="sy1">></span>, Alloc<span class="sy1">></span> <span class="sy4">:</span> <a href="cpp-types-integral_constant.html"><span class="kw649">std::<span class="me2">true_type</span></span></a> <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-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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<p><span class="t-lc"><a href="cpp-memory-uses_allocator.html">std::uses_allocator</a></span> 的此特化告知其他库组件，所有 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 类型对象支持 <i>uses-allocator 构造</i>，即使它们无嵌套的 <code>allocator_type</code> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</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 uses-allocator 构造 ，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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<h2><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::integral_constant">继承自 <a href="cpp-types-integral_constant.html"><span style="font-size:0.7em; line-height:130%">std::</span>integral_constant</a></span></h2>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.B8.B8.E9.87.8F">成员常量</span></h3>
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<div><span class="t-lines"><span>value</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span><br />
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<span class="t-mark">(公开静态成员常量)</span></td>
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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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<div><span class="t-lines"><span>operator bool</span></span></div>
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</td>
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<td>转换对象为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> ，返回 <code>value</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>operator()</span></span></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
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<td>返回 <code>value</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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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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<td>类型</td>
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<td>定义</td>
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<td><code>value_type</code></td>
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<td><code>bool</code></td>
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<td><code>type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-integral_constant.html"><span class="kw647">std::<span class="me2">integral_constant</span></span></a><span class="sy1"><</span><span class="kw4">bool</span>, value<span class="sy1">></span></span></span></td>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div><a href="cpp-memory-uses_allocator.html"><span class="t-lines"><span>uses_allocator</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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<td>检查指定的类型是否支持使用分配器的构造<br />
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<span class="t-mark">(类模板)</span></td>
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