94 lines
8.3 KiB
HTML
94 lines
8.3 KiB
HTML
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<title>std::experimental::ranges::CommonReference</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_experimental_ranges_concepts_CommonReference 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::experimental::ranges::</span>CommonReference</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a>‎ | <a href="cpp-experimental-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-experimental-ranges-concepts.html"><experimental/ranges/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="kw1">class</span> U <span class="sy1">></span><br /></span>
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<p>concept <span class="kw4">bool</span> CommonReference <span class="sy1">=</span><br />
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<a href="cpp-experimental-ranges-concepts-Same.html"><span class="kw2530">ranges::<span class="me2">Same</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">></span>, ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>U, T<span class="sy1">>></span> <span class="sy3">&&</span><br />
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<a href="cpp-experimental-ranges-concepts-ConvertibleTo.html"><span class="kw2532">ranges::<span class="me2">ConvertibleTo</span></span></a><span class="sy1"><</span>T, ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">>></span> <span class="sy3">&&</span><br /></p>
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<a href="cpp-experimental-ranges-concepts-ConvertibleTo.html"><span class="kw2532">ranges::<span class="me2">ConvertibleTo</span></span></a><span class="sy1"><</span>U, ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">>></span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-ranges-ts t-mark-ts">(范围 TS)</span></td>
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<p>概念 <code>CommonReference<T, U></code> 指定二个类型 <code>T</code> 与 <code>U</code> 共享都能转换到的<i>共用引用类型</i>（由 <span class="t-lc">ranges::common_reference_t</span> 计算）。</p>
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<p><code>CommonReference<T, U></code> 仅若满足下列条件才得到满足。给定表达式 <code>t</code> 和 <code>u</code> 使得 <span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span></span></span> 为 <code>T</code> 而 <span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span><span class="br0">(</span>u<span class="br0">)</span><span class="br0">)</span></span></span> 为 <code>U</code> ，</p>
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<ul>
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<li>若且唯若 <code>t</code> 为保持相等性的表达式， <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span></span></span> 才等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span></span></span> ；且</li>
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<li>若且唯若 <code>u</code> 为保持相等性的表达式， <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">></span><span class="br0">(</span>u<span class="br0">)</span></span></span> 才等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">common_reference_t</span><span class="sy1"><</span>T, U<span class="sy1">></span><span class="br0">(</span>u<span class="br0">)</span></span></span> 。</li>
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</ul>
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<p>换言之，转换到共用引用类型必须不改变原表达式的相等性保持属性。</p>
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<h3><span class="mw-headline" id=".E7.9B.B8.E7.AD.89.E6.80.A7.E4.BF.9D.E6.8C.81">相等性保持</span></h3>
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<p>若表达式对给定的相等输入产生相等输出，则它<i>保持相等性</i>。</p>
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<ul>
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<li>表达式的输入由其运算数组成。</li>
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<li>表达式的输出由其结果和表达式所修改的所有运算数（若存在）组成。</li>
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<p>进一步要求每个要求保持相等性的表达式都<i>稳定</i>：这种表达式带相同输入对象的二次求值必须拥有相等的输出，而无任何对这些输入对象的显式中间修改。</p>
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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-experimental-ranges-type_traits-common_reference.html"><span class="t-lines"><span>common_reference</span></span></a></div>
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<td>确定类型集合的公共引用类型<br />
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<span class="t-mark">(类模板)</span></td>
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<div><a href="cpp-experimental-ranges-concepts-Common.html"><span class="t-lines"><span>Common</span></span></a></div>
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<td>指定两个类型共有一个公共类型<br />
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<span class="t-mark">(概念)</span></td>
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<div><a href="cpp-experimental-ranges-type_traits-common_type.html"><span class="t-lines"><span>common_type</span></span></a></div>
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<td>确定类型集合的公共类型<br />
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<span class="t-mark">(类模板)</span></td>
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