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88 lines
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<title>std::experimental::ranges::WeaklyEqualityComparableWith</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::ranges::</span>WeaklyEqualityComparableWith</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> WeaklyEqualityComparableWith <span class="sy1">=</span><br />
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requires<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> t,<br />
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<span class="kw4">const</span> <a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="sy3">&</span> u<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="br0">{</span> t <span class="sy1">==</span> u <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> <a href="cpp-experimental-ranges-concepts-Boolean.html"><span class="kw2541">ranges::<span class="me2">Boolean</span></span></a><span class="sy3">&&</span><span class="sy4">;</span><br />
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<span class="br0">{</span> t <span class="sy3">!</span><span class="sy1">=</span> u <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> <a href="cpp-experimental-ranges-concepts-Boolean.html"><span class="kw2541">ranges::<span class="me2">Boolean</span></span></a><span class="sy3">&&</span><span class="sy4">;</span><br />
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<span class="br0">{</span> u <span class="sy1">==</span> t <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> <a href="cpp-experimental-ranges-concepts-Boolean.html"><span class="kw2541">ranges::<span class="me2">Boolean</span></span></a><span class="sy3">&&</span><span class="sy4">;</span><br />
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<span class="br0">{</span> u <span class="sy3">!</span><span class="sy1">=</span> t <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> <a href="cpp-experimental-ranges-concepts-Boolean.html"><span class="kw2541">ranges::<span class="me2">Boolean</span></span></a><span class="sy3">&&</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</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>WeaklyEqualityComparableWith<T, U></code> 指定能用 <code>==</code> 和 <code>!=</code> 相互比较（以任一顺序） <code>T</code> 类型对象和 <code>U</code> 类型对象的相等性，而比较结果一致。更正式地说， <code>WeaklyEqualityComparableWith<T, U></code> 仅若满足下列条件才得到满足。给定</p>
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<ul>
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<li><code>t</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span> 类型左值，和</li>
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<li><code>u</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>U<span class="sy1">></span></span></span> 类型左值</li>
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</ul>
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<p>下列为真：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">t <span class="sy1">==</span> u</span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp">u <span class="sy1">==</span> t</span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp">t <span class="sy3">!</span><span class="sy1">=</span> u</span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp">u <span class="sy3">!</span><span class="sy1">=</span> t</span></span> 拥有相同的定义域；</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span><span class="br0">(</span>u <span class="sy1">==</span> t<span class="br0">)</span> <span class="sy1">==</span> <span class="kw4">bool</span><span class="br0">(</span>t <span class="sy1">==</span> u<span class="br0">)</span></span></span> ；</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span><span class="br0">(</span>t <span class="sy3">!</span><span class="sy1">=</span> u<span class="br0">)</span> <span class="sy1">==</span> <span class="sy3">!</span><span class="kw4">bool</span><span class="br0">(</span>t <span class="sy1">==</span> u<span class="br0">)</span></span></span> ；且</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span><span class="br0">(</span>u <span class="sy3">!</span><span class="sy1">=</span> t<span class="br0">)</span> <span class="sy1">==</span> <span class="kw4">bool</span><span class="br0">(</span>t <span class="sy3">!</span><span class="sy1">=</span> u<span class="br0">)</span></span></span> 。</li>
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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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<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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</ul>
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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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<p>除非另外提醒，每个用于 <i>requires 表达式</i>中的表达式都要求保持相等性且稳定，而表达式的求值必须只修改其非常运算数。必须不修改常运算数。</p>
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<h3><span class="mw-headline" id=".E9.9A.90.E5.BC.8F.E8.A1.A8.E8.BE.BE.E5.BC.8F.E5.8F.98.E7.A7.8D">隐式表达式变种</span></h3>
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<p>使用不修改某 const 左值运算数的表达式的 <i>requires 表达式</i>亦隐式要求该表达式的额外变种对给定运算数接受非 const 左值或（可为 const 的）右值，除非以有区别的语义显式要求这种表达式变种。这些<i>隐式表达式变种</i>必须符合与声明的表达式的相同的语义。不指定实现以何种程度校验变种的语法。</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-concepts-EqualityComparable.html"><span class="t-lines"><span>EqualityComparable</span><span>EqualityComparableWith</span></span></a></div>
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<td>指定运算符 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">==</span></span></span> 是等价关系<br />
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<span class="t-mark">(概念)</span></td>
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