97 lines
8.6 KiB
HTML
97 lines
8.6 KiB
HTML
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<title>operator==(std::ranges::take_view::sentinel<Const>)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_take_view_sentinel_operator_cmp skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">operator==<small>(std::ranges::take_view::<i>sentinel</i><Const>)</small></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</a>‎ | <a href="cpp-ranges-take_view.html">take view</a>‎ | <a href="cpp-ranges-take_view-sentinel.html">sentinel</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span><br /></span>
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<p> operator<span class="sy1">==</span><span class="br0">(</span> <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>Base<span class="sy1">>></span><span class="sy3">&</span> y,<br /></p>
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<span class="kw4">const</span> <span class="coMULTI">/*sentinel*/</span><span class="sy3">&</span> x <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw4">bool</span> OtherC <span class="sy1">=</span> <span class="sy3">!</span>Const <span class="sy1">></span><br /></span>
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<p> requires std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>Base<span class="sy1">></span>,<br />
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ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span><span class="coMULTI">/*add-const-if*/</span><span class="sy1"><</span>OtherC, V<span class="sy1">>>></span><br />
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<span class="kw1">friend</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span> <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span><br />
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<span class="coMULTI">/*add-const-if*/</span><span class="sy1"><</span>OtherC, V<span class="sy1">>>></span><span class="sy3">&</span> y,<br /></p>
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<span class="kw4">const</span> <span class="coMULTI">/*sentinel*/</span><span class="sy3">&</span> x <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p>将 <span class="t-c"><span class="mw-geshi cpp source-cpp">take_view<span class="sy4">::</span><span class="coMULTI">/*sentinel*/</span></span></span> 与 <span class="t-lc">std::counted_iterator</span> （常通过调用 <a href="cpp-ranges-take_view-begin.html"><tt>take_view::begin</tt></a> 获得）比较。</p>
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<p>若 <code>y</code> 指向第 N 元素（其中 N 为传递给 <a href="cpp-ranges-take_view-take_view.html"><code>take_view</code> 的构造函数</a>的数）后一位置，或抵达了底层视图末尾则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>仅用于阐释的别名模板 <code><i>add-const-if</i></code> 定义为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw4">bool</span> C, <span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">using</span> <span class="coMULTI">/*add-const-if*/</span> <span class="sy1">=</span> <a href="cpp-types-conditional.html"><span class="kw634">std::<span class="me2">conditional_t</span></span></a><span class="sy1"><</span>C, <span class="kw4">const</span> T, T<span class="sy1">></span><span class="sy4">;</span></span></span> 。</p>
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<p>这些函数对通常<a href="cpp-language-unqualified_lookup.html">无限定</a>或<a href="cpp-language-qualified_lookup.html">有限定查找</a>不可见，而只能在 <code>std::ranges::take_view::<i>sentinel</i><Const></code> 为参数的关联类时由<a href="cpp-language-adl.html">实参依赖查找</a>找到。</p>
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<p><code>!=</code> 运算符从 <code>operator==</code> <a href="cpp-language-operators.html#.E5.85.B3.E7.B3.BB.E8.BF.90.E7.AE.97.E7.AC.A6">合成</a>。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>y</td>
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<td>-</td>
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<td>要比较的 <span class="t-lc">std::counted_iterator</span></td>
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</tr>
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<tr class="t-par">
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<td>x</td>
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<td>-</td>
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<td>要比较的哨位</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">y.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span> <span class="sy3">||</span> y.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> x.<span class="me1">end_</span></span></span> ，其中 <code><i>end_</i></code> 代表底层哨位。</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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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3449">LWG 3449</a></td>
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<td>C++20</td>
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<td>不支持相异 const 限定的 <code>take_view</code> 的迭代器与哨位间的比较</td>
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<td>使得在可能时支持</td>
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</tr>
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</table>
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