149 lines
15 KiB
HTML
149 lines
15 KiB
HTML
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<title>std::ranges::views::all, std::ranges::views::all_t</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_all_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::views::</span>all, <span style="font-size:0.7em; line-height:130%">std::ranges::views::</span>all_t</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>定义于头文件 <code><a href="cpp-header-ranges.html"><ranges></a></code></div>
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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">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/*unspecified*/</span> all <span class="sy1">=</span> <span class="coMULTI">/*unspecified*/</span><span class="sy4">;</span></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>ranges<span class="sy4">::</span><span class="me2">viewable_range</span> R<span class="sy1">></span><br />
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<span class="kw1">using</span> all_t <span class="sy1">=</span> decltype<span class="br0">(</span>views<span class="sy4">::</span><span class="me2">all</span><span class="br0">(</span><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></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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<div class="t-li1"><span class="t-li">1)</span> 返回包含其 <a href="cpp-ranges-range.html"><code>range</code></a> 参数的所有元素的 <a href="cpp-ranges-view.html"><code>view</code></a> 的<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>(亦为<a href="cpp-ranges.html#.E8.8C.83.E5.9B.B4.E9.80.82.E9.85.8D.E5.99.A8.E9.97.AD.E5.8C.85.E5.AF.B9.E8.B1.A1">范围适配器闭包对象</a>)。<br />
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">all</span><span class="br0">(</span>e<span class="br0">)</span></span></span> 表达式等价于:</p>
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<ul>
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<li>隐式转换 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><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></span></span> 纯右值,若结果类型实现 <a href="cpp-ranges-view.html"><code>view</code></a> 。</li>
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<li>否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">ref_view</span><span class="br0">{</span>e<span class="br0">}</span></span></span> ,若该表达式为良构。</li>
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<li>否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">owning_view</span><span class="br0">{</span>e<span class="br0">}</span></span></span> 。</li>
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</ul>
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</div>
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<div class="t-li1"><span class="t-li">2)</span> 计算 <a href="cpp-ranges-viewable_range.html"><code>viewable_range</code></a> 类型的适合 <a href="cpp-ranges-view.html"><code>view</code></a> 类型。</div>
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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=".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 <ranges></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <type_traits></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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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v<span class="br0">{</span><span class="nu0">0</span>,<span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span><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> n <span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">all</span><span class="br0">(</span>v<span class="br0">)</span> <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">take</span><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="br0">)</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> n <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<span class="br0">}</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>
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decltype<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">single</span><span class="br0">(</span><span class="nu0">42</span><span class="br0">)</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">single_view</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span>
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<span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>
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decltype<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">all</span><span class="br0">(</span>v<span class="br0">)</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">ref_view</span><span class="sy1"><</span><a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <a href="cpp-memory-allocator.html"><span class="kw700">std::<span class="me2">allocator</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">>>></span>
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<span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>
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decltype<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">all</span><span class="br0">(</span>a<span class="br0">)</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">ref_view</span><span class="sy1"><</span><span class="kw4">int</span> <span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy1">></span>
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<span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>
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decltype<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span><span class="br0">{</span><a href="cpp-iterator-begin.html"><span class="kw676">std::<span class="me2">begin</span></span></a><span class="br0">(</span>a<span class="br0">)</span><span class="sy2">+</span><span class="nu0">1</span>, <a href="cpp-iterator-end.html"><span class="kw680">std::<span class="me2">end</span></span></a><span class="br0">(</span>a<span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">}</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy2">*</span>, <span class="kw4">int</span><span class="sy2">*</span>, std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange_kind</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy1">></span>
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<span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<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;">
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<div class="text source-text">
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<pre class="de1">0 1</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://wg21.link/P2415R2">P2415R2</a></td>
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<td>C++20</td>
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<td><code>views::all</code> 对非 <a href="cpp-ranges-view.html"><code>view</code></a> 右值 <a href="cpp-ranges-range.html"><code>range</code></a> 返回 <code>subrange</code></td>
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<td>对其返回 <code>owning_view</code></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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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-empty_view.html"><span class="t-lines"><span>ranges::empty_view</span><span>views::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>无元素的空 <a href="cpp-ranges-view.html"><code>view</code></a><br />
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<span class="t-mark">(类模板)</span> <span class="t-mark">(变量模板)</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-single_view.html"><span class="t-lines"><span>ranges::single_view</span><span>views::single</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>含有具有指定值的单个元素的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
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<span class="t-mark">(类模板)</span> <span class="t-mark">(定制点对象)</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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</body>
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