100 lines
6.4 KiB
HTML
100 lines
6.4 KiB
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::semiregular</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_concepts_semiregular 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>semiregular</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-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> T<span class="sy1">></span><br />
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concept semiregular <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">copyable</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>T<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><code>semiregular</code> 概念指定类型既为可复制亦为可默认构造。表现类似如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> 的内建类型的类型满足它，除了它们不需要支持以 <code>==</code> 比较。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <concepts></span>
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<span class="co2">#include <iostream></span>
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<span class="kw1">template</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">semiregular</span> T<span class="sy1">></span>
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<span class="co1">// 版权所有 Alexander Stepanov</span>
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<span class="co1">// 概念是 T 上的要求</span>
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<span class="co1">// T 上的要求： T 为半正则</span>
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<span class="co1">// T a(b) 或 T a = b => 复制构造函数； T a => 默认构造函数； a = b => 赋值；</span>
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<span class="kw1">struct</span> Single <span class="br0">{</span>
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T value<span class="sy4">;</span>
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<span class="co1">// 隐式声明的特殊成员函数表现类似以下定义，除了它们可以拥有额外属性。</span>
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<span class="co1">// Single(const Single& x) : value(x.value){}</span>
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<span class="co1">// Single(){}</span>
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<span class="co1">// ~Single(){}</span>
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<span class="co1">// Single& operator=(const Single& x) { value = x.value; return *this; }</span>
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<span class="br0">}</span><span class="sy4">;</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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Single<span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> myInt1<span class="sy4">;</span>
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myInt1.<span class="me1">value</span> <span class="sy1">=</span> <span class="nu0">4</span><span class="sy4">;</span>
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Single<span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> myInt2<span class="br0">(</span>myInt1<span class="br0">)</span><span class="sy4">;</span>
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Single<span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> myInt3<span class="sy4">;</span>
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myInt3 <span class="sy1">=</span> myInt2<span class="sy4">;</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> myInt1.<span class="me1">value</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> myInt2.<span class="me1">value</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> myInt3.<span class="me1">value</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></pre></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">4 4 4</pre></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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<div><a href="cpp-concepts-regular.html"><span class="t-lines"><span>regular</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>指定类型为正则，即它既为 <strong class="selflink"><code>semiregular</code></strong> 亦为 <a href="cpp-concepts-equality_comparable.html"><code>equality_comparable</code></a><br />
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<span class="t-mark">(概念)</span></td>
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