365 lines
29 KiB
HTML
365 lines
29 KiB
HTML
<!DOCTYPE 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::ranges::views::elements, std::ranges::elements_view</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_elements_view 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><span style="font-size:0.7em; line-height:130%">views::</span>elements, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>elements_view</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-ranges.html">ranges</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>定义于头文件 <code><a href="cpp-header-ranges.html"><ranges></a></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">input_range</span> V, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></span>
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<p> requires<br />
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view<span class="sy1"><</span>V<span class="sy1">></span> <span class="sy3">&&</span><br />
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__HasTupleElement<span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">range_value_t</span><span class="sy1"><</span>V<span class="sy1">></span>, N<span class="sy1">></span> <span class="sy3">&&</span><br />
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__HasTupleElement<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>ranges<span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1"><</span>V<span class="sy1">>></span>, N<span class="sy1">></span> <span class="sy3">&&</span><br />
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__ReturnableElement<span class="sy1"><<</span>ranges<span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1"><</span>V<span class="sy1">></span>, N<span class="sy1">></span><br /></p>
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<span class="kw1">class</span> elements_view <span class="sy4">:</span> <span class="kw1">public</span> ranges<span class="sy4">::</span><span class="me2">view_interface</span><span class="sy1"><</span>elements_view<span class="sy1"><</span>V, N<span class="sy1">>></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">namespace</span> views <span class="br0">{</span><br /></span>
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<p> <span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/*unspecified*/</span> elements <span class="sy1">=</span> <span class="coMULTI">/*unspecified*/</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</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>
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<tr class="t-dcl-sep">
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<td></td>
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<div>调用签名</div>
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</td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">viewable_range</span> R <span class="sy1">></span><br /></span>
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<p> requires <span class="coMULTI">/* see below */</span><br /></p>
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">view</span> <span class="kw4">auto</span> elements<span class="sy1"><</span>N<span class="sy1">></span><span class="br0">(</span> R<span class="sy3">&&</span> r <span class="br0">)</span><span class="sy4">;</span></div>
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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></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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<div>辅助概念</div>
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</td>
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<td></td>
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<td></td>
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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, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></span>
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<p>concept __HasTupleElement <span class="sy1">=</span> <span class="co1">// 仅用于阐释</span><br />
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requires<span class="br0">(</span>T t<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_size.html"><span class="kw1101">std::<span class="me2">tuple_size</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy4">;</span><br />
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requires N <span class="sy1"><</span> <a href="cpp-utility-tuple-tuple_size.html"><span class="kw1102">std::<span class="me2">tuple_size_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">;</span><br />
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<span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span>N, T<span class="sy1">></span><span class="sy4">;</span><br />
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<span class="br0">{</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span>N<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span> <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span><span class="kw4">const</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span>N, T<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></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>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<td>
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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, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></span>
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<p>concept __ReturnableElement <span class="sy1">=</span> <span class="co1">// 仅用于阐释</span><br /></p>
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<a href="cpp-types-is_reference.html"><span class="kw481">std::<span class="me2">is_reference_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">||</span> std<span class="sy4">::</span><span class="me2">move_constructible</span><span class="sy1"><</span><a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span>N, T<span class="sy1">>></span><span class="sy4">;</span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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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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<div class="t-li1"><span class="t-li">1)</span> 接收<i>元组式</i>值的 <a href="cpp-ranges-view.html"><code>view</code></a> ，并产生<i>值类型</i>为适配视图的值类型的第 <code>N</code> 元素<i>的视图。</i></div>
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<div class="t-li1"><span class="t-li">2)</span> <code>views::elements</code> 的每个特化均为<a href="cpp-ranges.html#.E8.8C.83.E5.9B.B4.E9.80.82.E9.85.8D.E5.99.A8.E5.AF.B9.E8.B1.A1">范围适配器对象</a>。对于任何适合的表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与常量表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">M</span></span>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">views​<span class="sy4">::</span>​elements<span class="sy1"><</span>M<span class="sy1">></span><span class="br0">(</span>e<span class="br0">)</span></span></span> <i>表达式等价</i>于 <span class="t-c"><span class="mw-geshi cpp source-cpp">elements_view<span class="sy1"><</span>views​<span class="sy4">::</span>​all_t<span class="sy1"><</span>decltype<span class="br0">(</span><span class="br0">(</span>e<span class="br0">)</span><span class="br0">)</span><span class="sy1">></span>, M<span class="sy1">></span><span class="br0">{</span>e<span class="br0">}</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 确保底层视图的元素是<i>元组式</i>值。</div>
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<div class="t-li1"><span class="t-li">4)</span> 确保不能返回悬垂引用。</div>
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<p><code>elements_view</code> 在底层视图 <code>V</code> 实现 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a>、 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a>、 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a>、 <a href="cpp-ranges-input_range.html"><code>input_range</code></a>、 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 及 <a href="cpp-ranges-sized_range.html"><code>sized_range</code></a> 时实现对应的概念。</p>
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<h3><span class="mw-headline" id=".E8.A1.A8.E8.BE.BE.E5.BC.8F.E7.AD.89.E4.BB.B7">表达式等价</span></h3>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 拥有相同效果，均为<a href="cpp-language-noexcept_spec.html">潜在抛出</a>或均非潜在抛出（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>e<span class="br0">)</span> <span class="sy1">==</span> <span class="kw1">noexcept</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ），且均为<a href="cpp-language-constant_expression.html">常量子表达式</a>或均非常量子表达式。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-ranges-elements_view-elements_view.html"><span class="t-lines"><span>(构造函数)</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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</div>
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</td>
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<td>构造 <code>elements_view</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-base.html"><span class="t-lines"><span>base</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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</div>
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</td>
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<td>返回底层（适配的）视图的副本<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-begin.html"><span class="t-lines"><span>begin</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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</div>
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</td>
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<td>返回指向起始的迭代器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-end.html"><span class="t-lines"><span>end</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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</div>
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</td>
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<td>返回指向末尾的迭代器或哨位<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-size.html"><span class="t-lines"><span>size</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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</div>
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</td>
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<td>返回元素数，只要底层（适配的）范围满足 <a href="cpp-ranges-sized_range.html"><code>sized_range</code></a><br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::ranges::view_interface">继承自 <span class="t-lc">std::ranges::view_interface</span></span></h5>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-empty.html"><span class="t-lines"><span>empty</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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</div>
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</td>
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<td>返回视图是否为空。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-operator_bool.html"><span class="t-lines"><span>operator bool</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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</div>
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</td>
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<td>返回派生视图是否为非空。若 <span class="t-lc">ranges::empty</span> 可应用于它则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-front.html"><span class="t-lines"><span>front</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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</div>
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</td>
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<td>返回派生视图中的首元素。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-back.html"><span class="t-lines"><span>back</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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</div>
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</td>
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<td>返回派生视图中的末元素。若视图满足 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 与 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-operator_at.html"><span class="t-lines"><span>operator[]</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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</div>
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</td>
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<td>返回派生视图中的第 n 个元素。若视图满足 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.B5.8C.E5.A5.97.E7.B1.BB">嵌套类</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-iterator.html"><i><span class="t-lines"><span>iterator</span></span></i></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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</div>
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</td>
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<td>迭代器类型<br />
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<span class="t-mark">(仅用于阐释的成员类模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-elements_view-sentinel.html"><i><span class="t-lines"><span>sentinel</span></span></i></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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</div>
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</td>
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<td>哨位类型<br />
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<span class="t-mark">(仅用于阐释的成员类模板)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E6.A8.A1.E6.9D.BF">辅助模板</span></h3>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<td>
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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, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">></span><br /></span>
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<p><span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> enable_borrowed_range<span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">elements_view</span><span class="sy1"><</span>T, N<span class="sy1">>></span> <span class="sy1">=</span><br /></p>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">enable_borrowed_range</span><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">;</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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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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</tr>
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</tbody>
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</table>
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<p><a href="cpp-ranges-borrowed_range.html"><tt>std::ranges::enable_borrowed_range</tt></a> 的此特化使得 <code>elements_view</code> 在底层视图满足 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a> 时满足它。</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="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <ranges></span>
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<span class="co2">#include <tuple></span>
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<span class="co2">#include <vector></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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<span class="kw4">const</span> <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">char</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">>></span> vt <span class="br0">{</span>
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<span class="br0">{</span><span class="nu0">1</span>, <span class="st0">'A'</span>, <span class="st0">"α"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="nu0">2</span>, <span class="st0">'B'</span>, <span class="st0">"β"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="nu0">3</span>, <span class="st0">'C'</span>, <span class="st0">"γ"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="nu0">4</span>, <span class="st0">'D'</span>, <span class="st0">"δ"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="nu0">5</span>, <span class="st0">'E'</span>, <span class="st0">"ε"</span><span class="br0">}</span>,
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> <span class="kw4">const</span> e<span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">elements</span><span class="sy1"><</span><span class="nu0">0</span><span class="sy1">></span><span class="br0">(</span>vt<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> e <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</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> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">char</span> <span class="kw4">const</span> e<span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">elements</span><span class="sy1"><</span><span class="nu0">1</span><span class="sy1">></span><span class="br0">(</span>vt<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> e <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</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> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> <span class="kw4">const</span><span class="sy3">&</span> e<span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">elements</span><span class="sy1"><</span><span class="nu0">2</span><span class="sy1">></span><span class="br0">(</span>vt<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> e <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</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> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">1 2 3 4 5
|
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A B C D E
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α β γ δ ε</pre></div>
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</div>
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</div>
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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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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3494">LWG 3494</a></td>
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<td>C++20</td>
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<td><code>elements_view</code> 始终不是 <code>borrowed_range</code></td>
|
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<td>若底层视图是 <code>borrowed_range</code> 则它是</td>
|
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3502">LWG 3502</a></td>
|
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<td>C++20</td>
|
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<td>能从 <code>elements_view</code> 获得悬垂引用</td>
|
|
<td>禁止这种用法</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-keys_view.html"><span class="t-lines"><span>ranges::keys_view</span><span>views::keys</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>
|
|
</div>
|
|
</td>
|
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<td>选取 pair 式值组成的 <a href="cpp-ranges-view.html"><code>view</code></a> 并产生每个 pair 的第一元素的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
|
|
<span class="t-mark">(类模板)</span> <span class="t-mark">(范围适配器对象)</span></td>
|
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</tr>
|
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<tr class="t-dsc">
|
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<td>
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<div class="t-dsc-member-div">
|
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<div><a href="cpp-ranges-values_view.html"><span class="t-lines"><span>ranges::values_view</span><span>views::values</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
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</div>
|
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</td>
|
|
<td>选取 pair 式值组成的 <a href="cpp-ranges-view.html"><code>view</code></a> 并产生每个 pair 的第二元素的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
|
|
<span class="t-mark">(类模板)</span> <span class="t-mark">(范围适配器对象)</span></td>
|
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</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-numeric-valarray-slice.html"><span class="t-lines"><span>slice</span></span></a></div>
|
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</div>
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</td>
|
|
<td>valarray 的 BLAS 式切片：起始下标、长度、跨度<br />
|
|
<span class="t-mark">(类)</span></td>
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</tr>
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</table>
|
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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