77 lines
5.9 KiB
HTML
77 lines
5.9 KiB
HTML
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<title>std::ranges::viewable_range</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_viewable_range 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::ranges::</span>viewable_range</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-ranges.html"><ranges></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 /></span>
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<p>concept viewable_range <span class="sy1">=</span><br />
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ranges<span class="sy4">::</span><span class="me2">range</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span><br />
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<span class="br0">(</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">view</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>T<span class="sy1">>></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>T<span class="sy1">></span>, T<span class="sy1">></span><span class="br0">)</span> <span class="sy3">||</span><br />
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<span class="br0">(</span><span class="sy3">!</span>ranges<span class="sy4">::</span><span class="me2">view</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>T<span class="sy1">>></span> <span class="sy3">&&</span><br />
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<span class="br0">(</span><a href="cpp-types-is_lvalue_reference.html"><span class="kw465">std::<span class="me2">is_lvalue_reference_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">||</span><br /></p>
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<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">movable</span><span class="sy1"><</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> <span class="sy3">!</span><span class="coMULTI">/*is-initializer-list*/</span><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</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>viewable_range</code> 概念是 <a href="cpp-ranges-range.html"><code>range</code></a> 的细化，它描述能安全转换成 <a href="cpp-ranges-view.html"><code>view</code></a> 的范围。</p>
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<p>常量 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*is-initializer-list*/</span><span class="sy1"><</span>T<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 当且仅当 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>T<span class="sy1">></span></span></span> 为 <span class="t-lc"><a href="cpp-utility-initializer_list.html">std::initializer_list</a></span> 的特化。</p>
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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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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3481">LWG 3481</a></td>
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<td>C++20</td>
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<td><code>viewable_range</code> 曾接受仅移动视图的左值</td>
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<td>拒绝</td>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2415R2">P2415R2</a></td>
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<td>C++20</td>
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<td><code>viewable_range</code> 仅接受作为 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a> 的非 <a href="cpp-ranges-view.html"><code>view</code></a> 右值</td>
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<td>接受更多类型</td>
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