150 lines
11 KiB
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150 lines
11 KiB
HTML
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<title>std::tuple_element<std::ranges::subrange></title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_subrange_tuple_element 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::</span>tuple_element<small><std::ranges::subrange></small></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>‎ | <a href="cpp-ranges-subrange.html">subrange</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> I, <span class="kw1">class</span> S, ranges<span class="sy4">::</span><span class="me2">subrange_kind</span> K <span class="sy1">></span><br />
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<span class="kw1">struct</span> tuple_element<span class="sy1"><</span><span class="nu0">0</span>, ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, S, K<span class="sy1">>></span><span class="sy4">;</span></span></div>
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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="kw1">class</span> I, <span class="kw1">class</span> S, ranges<span class="sy4">::</span><span class="me2">subrange_kind</span> K <span class="sy1">></span><br />
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<span class="kw1">struct</span> tuple_element<span class="sy1"><</span><span class="nu0">0</span>, <span class="kw4">const</span> ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, S, K<span class="sy1">>></span><span class="sy4">;</span></span></div>
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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><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> I, <span class="kw1">class</span> S, ranges<span class="sy4">::</span><span class="me2">subrange_kind</span> K <span class="sy1">></span><br />
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<span class="kw1">struct</span> tuple_element<span class="sy1"><</span><span class="nu0">1</span>, ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, S, K<span class="sy1">>></span><span class="sy4">;</span></span></div>
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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 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> <span class="kw1">class</span> I, <span class="kw1">class</span> S, ranges<span class="sy4">::</span><span class="me2">subrange_kind</span> K <span class="sy1">></span><br />
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<span class="kw1">struct</span> tuple_element<span class="sy1"><</span><span class="nu0">1</span>, <span class="kw4">const</span> ranges<span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, S, K<span class="sy1">>></span><span class="sy4">;</span></span></div>
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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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<p><a href="cpp-utility-tuple_element.html"><tt>std::tuple_element</tt></a> 对 <span class="t-lc">std::ranges::subrange</span> 的部分特化用元组式语法提供 <code>subrange</code> 的迭代器或哨位类型的编译时访问。它们是为结构化绑定支持提供的。</p>
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<div class="t-li1"><span class="t-li">1-2)</span> 获得迭代器类型，即 <code>I</code> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 获得哨位类型，即 <code>S</code> 。</div>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<tr class="t-dsc">
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<td><code>type</code></td>
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<td><span class="t-v">(1-2)</span> <code>I</code><br />
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<span class="t-v">(3-4)</span> <code>S</code></td>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>由于 <code>subrange</code> 的 <a href="cpp-ranges-subrange-get.html"><code>get</code></a> 函数按值返回迭代器与哨位，在 为 const 限定（但非 volatile 限定）时不添加 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> 限定符到结果类型。</p>
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<p>若 <code>subrange</code> 为 volatile 限定，则结果类型亦为 volatile 限定，因为使用了对 volatile 或 const volatile 类型的部分特化。这种使用被弃用。</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 <iterator></span>
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<span class="co2">#include <list></span>
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<span class="co2">#include <ranges></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-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> list<span class="br0">{</span><span class="nu0">3</span>, <span class="nu0">1</span>, <span class="nu0">4</span>, <span class="nu0">1</span>, <span class="nu0">5</span>, <span class="nu0">9</span>, <span class="nu0">2</span>, <span class="nu0">6</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span> subrange<span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">counted_iterator</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>list<span class="br0">)</span>, <span class="nu0">4</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">default_sentinel</span>
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<span class="br0">}</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span>
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<a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><span class="sy1"><</span>
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<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><span class="nu0">0</span>, decltype<span class="br0">(</span>subrange<span class="br0">)</span><span class="sy1">></span>,
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<span class="co1">// 实现定义的类型：</span>
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std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>std<span class="sy4">::</span>_List_iterator<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="sy4">;</span>
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static_assert<span class="br0">(</span>
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<a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><span class="sy1"><</span>
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<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><span class="nu0">1</span>, decltype<span class="br0">(</span>subrange<span class="br0">)</span><span class="sy1">></span>,
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std<span class="sy4">::</span><span class="me2">default_sentinel_t</span>
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<span class="sy1">></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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<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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<td><a href="cpp-language-structured_binding.html">结构化绑定</a> <span class="t-mark-rev t-since-cxx17">(C++17)</span></td>
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<td>绑定指定的名字到初始化器的子对象或元组元素</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-utility-tuple_element.html"><span class="t-lines"><span>tuple_element</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>获得元组式类型的元素类型<br />
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<span class="t-mark">(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-subrange-tuple_size.html"><span class="t-lines"><span>std::tuple_size<span class="t-dsc-small"><std::ranges::subrange></span></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>获得 <span class="t-lc">std::ranges::subrange</span> 的组分数量<br />
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<span class="t-mark">(类模板特化)</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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