308 lines
28 KiB
HTML
308 lines
28 KiB
HTML
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<title>std::tuple_element</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_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</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-utility.html">utility</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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<td>
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<div>定义于头文件 <code><a href="cpp-header-tuple.html"><tuple></a></code></div>
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</td>
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<td></td>
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<td></td>
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<div>定义于头文件 <code><a href="cpp-header-array.html"><array></a></code></div>
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<td></td>
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<td></td>
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<td>
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<div>定义于头文件 <code><a href="cpp-header-utility.html"><utility></a></code></div>
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<td></td>
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<td></td>
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<tr class="t-dsc-header">
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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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<div><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="kw1">struct</span> tuple_element<span class="sy4">;</span> <span class="co1">// 不定义</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T <span class="sy1">></span><br /></span>
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<p><span class="kw1">struct</span> tuple_element<span class="sy1"><</span> I, <span class="kw4">const</span> T <span class="sy1">></span> <span class="br0">{</span><br />
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<span class="kw1">using</span> type <span class="sy1">=</span> <span class="kw1">typename</span><br />
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<a href="cpp-types-add_cv.html"><span class="kw601">std::<span class="me2">add_const</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span>I, T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">type</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>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T <span class="sy1">></span><br /></span>
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<p><span class="kw1">struct</span> tuple_element<span class="sy1"><</span> I, <span class="kw4">volatile</span> T <span class="sy1">></span> <span class="br0">{</span><br />
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<span class="kw1">using</span> type <span class="sy1">=</span> <span class="kw1">typename</span><br />
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<a href="cpp-types-add_cv.html"><span class="kw602">std::<span class="me2">add_volatile</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span>I, T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">type</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-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(C++20 中弃用)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T <span class="sy1">></span><br /></span>
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<p><span class="kw1">struct</span> tuple_element<span class="sy1"><</span> I, <span class="kw4">const</span> <span class="kw4">volatile</span> T <span class="sy1">></span> <span class="br0">{</span><br />
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<span class="kw1">using</span> type <span class="sy1">=</span> <span class="kw1">typename</span><br />
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<a href="cpp-types-add_cv.html"><span class="kw600">std::<span class="me2">add_cv</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span>I, T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">type</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>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(C++20 中弃用)</span></td>
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<td></td>
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<p>提供对元组式类型的元素类型的编译时下标访问。</p>
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<div class="t-li1"><span class="t-li">1)</span> 不定义主模板。要求显式（全）或部分特化以令类型为元组式。</div>
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<div class="t-li1"><span class="t-li">2-4)</span> 对 cv 限定类型的特化默认简单地添加对应的 cv 限定符。</div>
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<p><code>std::tuple_element</code> 与核心语言交互：它能在元组式情况下提供<a href="cpp-language-structured_binding.html">结构化绑定</a>支持。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</table>
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<h3><span class="mw-headline" id=".E7.89.B9.E5.8C.96">特化</span></h3>
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<p>标准库对标准库类型提供下列特化：</p>
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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-utility-tuple-tuple_element.html"><span class="t-lines"><span>std::tuple_element<span class="t-dsc-small"><std::tuple></span></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>获得指定元素的类型<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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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-pair-tuple_element.html"><span class="t-lines"><span>std::tuple_element<span class="t-dsc-small"><std::pair></span></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 <code>pair</code> 中元素的类型<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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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-array-tuple_element.html"><span class="t-lines"><span>std::tuple_element<span class="t-dsc-small"><std::array></span></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 <code>array</code> 元素的类型<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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<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_element.html"><span class="t-lines"><span>std::tuple_element<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> 的迭代器或哨位的类型<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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<p>用户可以对程序定义类型特化 <code>std::tuple_size</code> 以令它们为元组式。</p>
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<p>在 <code>get</code> 函数返回引用成员或到子对象的引用的通常情况下，只需要定制对 cv 无限定类型的特化。</p>
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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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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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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>type</td>
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<td>对标准特化，为元组式类型 <code>T</code> 的第 <code>I</code> 个元素，其中 <code>I</code> 在 [0, <span class="t-c"><span class="mw-geshi cpp source-cpp"><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">value</span></span></span>) 中</td>
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</table>
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<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E7.B1.BB.E5.9E.8B">辅助类型</span></h3>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-tuple.html"><tuple></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-cxx14">
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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><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T<span class="sy1">></span><br />
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<span class="kw1">using</span> tuple_element_t <span class="sy1">=</span> <span class="kw1">typename</span> tuple_element<span class="sy1"><</span>I, T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy4">;</span></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-cxx14">(C++14 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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<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 <array></span>
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<span class="co2">#include <cstddef></span>
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<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 <type_traits></span>
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<span class="co2">#include <utility></span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> T1, <span class="kw1">typename</span> T2, <span class="kw1">typename</span> T3<span class="sy1">></span>
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<span class="kw1">struct</span> Triple <span class="br0">{</span> T1 t1<span class="sy4">;</span> T2 t2<span class="sy4">;</span> T3 t3<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="co1">// A specialization of std::tuple_element for program-defined type Triple:</span>
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<span class="kw1">template</span> <span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">typename</span> T1, <span class="kw1">typename</span> T2, <span class="kw1">typename</span> T3<span class="sy1">></span>
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<span class="kw1">struct</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span>I, Triple<span class="sy1"><</span>T1, T2, T3<span class="sy1">>></span> <span class="br0">{</span> static_assert<span class="br0">(</span>I <span class="sy1"><</span> <span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> T1, <span class="kw1">typename</span> T2, <span class="kw1">typename</span> T3<span class="sy1">></span>
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<span class="kw1">struct</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span><span class="nu0">0</span>, Triple<span class="sy1"><</span>T1, T2, T3<span class="sy1">>></span> <span class="br0">{</span> <span class="kw1">using</span> type <span class="sy1">=</span> T1<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> T1, <span class="kw1">typename</span> T2, <span class="kw1">typename</span> T3<span class="sy1">></span>
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<span class="kw1">struct</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, Triple<span class="sy1"><</span>T1, T2, T3<span class="sy1">>></span> <span class="br0">{</span> <span class="kw1">using</span> type <span class="sy1">=</span> T2<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> T1, <span class="kw1">typename</span> T2, <span class="kw1">typename</span> T3<span class="sy1">></span>
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<span class="kw1">struct</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1099">std::<span class="me2">tuple_element</span></span></a><span class="sy1"><</span><span class="nu0">2</span>, Triple<span class="sy1"><</span>T1, T2, T3<span class="sy1">>></span> <span class="br0">{</span> <span class="kw1">using</span> type <span class="sy1">=</span> T3<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span>... <span class="me1">Args</span><span class="sy1">></span> <span class="kw1">struct</span> TripleTypes <span class="br0">{</span>
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static_assert<span class="br0">(</span><span class="nu0">3</span> <span class="sy1">==</span> sizeof...<span class="br0">(</span>Args<span class="br0">)</span>, <span class="st0">"Expected exactly 3 type names!"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">></span>
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<span class="kw1">using</span> type <span class="sy1">=</span> <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, Triple<span class="sy1"><</span>Args...<span class="sy1">>></span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</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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TripleTypes<span class="sy1"><</span><span class="kw4">char</span>, <span class="kw4">int</span>, <span class="kw4">float</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy1"><</span><span class="nu0">1</span><span class="sy1">></span> i<span class="br0">{</span><span class="nu0">42</span><span class="br0">}</span><span class="sy4">;</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> i <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">using</span> Tri <span class="sy1">=</span> Triple<span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">char</span>, <span class="kw4">short</span><span class="sy1">></span><span class="sy4">;</span> <span class="co1">//< Program-defined type</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><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><span class="nu0">0</span>, Tri<span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">></span> <span class="sy3">&&</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><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>, Tri<span class="sy1">></span>, <span class="kw4">char</span><span class="sy1">></span> <span class="sy3">&&</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><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">2</span>, Tri<span class="sy1">></span>, <span class="kw4">short</span><span class="sy1">></span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">using</span> Tuple <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>, <span class="kw4">short</span><span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><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><span class="nu0">0</span>, Tuple<span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">></span> <span class="sy3">&&</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><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>, Tuple<span class="sy1">></span>, <span class="kw4">char</span><span class="sy1">></span> <span class="sy3">&&</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><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">2</span>, Tuple<span class="sy1">></span>, <span class="kw4">short</span><span class="sy1">></span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">using</span> Array3 <span class="sy1">=</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="nu0">3</span><span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><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><span class="nu0">0</span>, Array3<span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">></span> <span class="sy3">&&</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><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>, Array3<span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">></span> <span class="sy3">&&</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><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">2</span>, Array3<span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">></span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">using</span> Pair <span class="sy1">=</span> <a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span>Tuple, Tri<span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><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><span class="nu0">0</span>, Pair<span class="sy1">></span>, Tuple<span class="sy1">></span> <span class="sy3">&&</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><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>, Pair<span class="sy1">></span>, Tri<span class="sy1">></span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">using</span> Sub <span class="sy1">=</span> 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><span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw589">std::<span class="me2">is_same_v</span></span></a><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><span class="nu0">0</span>, Sub<span class="sy1">></span>, <span class="kw4">int</span><span class="sy2">*</span><span class="sy1">></span> <span class="sy3">&&</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><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>, Sub<span class="sy1">></span>, <span class="kw4">int</span><span class="sy2">*</span><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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<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">42</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/issue2212">LWG 2212</a></td>
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<td>C++11</td>
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<td>未在某些头文件中要求对 cv 类型的特化，这导致歧义</td>
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<td>已要求</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><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_size.html"><span class="t-lines"><span>tuple_size</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数<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-utility-tuple-tuple_cat.html"><span class="t-lines"><span>tuple_cat</span></span></a></div>
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</div>
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</td>
|
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<td>通过连接任意数量的元组来创建一个<code>tuple</code><br />
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<span class="t-mark">(函数模板)</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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