57 lines
3.2 KiB
HTML
57 lines
3.2 KiB
HTML
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<title>std::equivalence_relation</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_concepts_equivalence_relation 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>equivalence_relation</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-concepts.html">concepts</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-concepts.html"><concepts></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> T, <span class="kw1">class</span> U <span class="sy1">></span><br />
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concept equivalence_relation <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">relation</span><span class="sy1"><</span>R, T, U<span class="sy1">></span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>概念 <code>equivalence_relation<R, T, U></code> 指定 <a href="cpp-concepts-relation.html"><code>relation</code></a> <code>R</code> 在其参数上施加等价关系。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E4.B9.89.E8.A6.81.E6.B1.82">语义要求</span></h3>
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<p>关系 <code>r</code> 为等价关系若</p>
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<ul>
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<li>它为自反：对于所有 <code>x</code> ， <code>r(x, x)</code> 为 <code>true</code> ；</li>
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<li>它为对称：对于所有 <code>a</code> 与 <code>b</code> ， <code>r(a, b)</code> 为 <code>true</code> 当且仅当 <code>r(b, a)</code> 为 <code>true</code> ；</li>
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<li>它为传递： <code>r(a, b) && r(b, c)</code> 蕴含 <code>r(a, c)</code> 。</li>
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</ul>
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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><a href="cpp-concepts-relation.html"><code>relation</code></a> 与 <code>equivalence_relation</code> 间的区别是纯语义的。</p>
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