194 lines
13 KiB
HTML
194 lines
13 KiB
HTML
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<title>std::ranges::elements_view<V,N>::iterator</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_elements_view_iterator 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::elements_view<V,N>::</span><i>iterator</i></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-elements_view.html">elements view</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw4">bool</span> Const <span class="sy1">></span><br />
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<span class="kw1">class</span> <span class="coMULTI">/*iterator*/</span><span class="sy4">;</span> <span class="co1">// 仅用于阐释</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-cxx20">(C++20 起)</span></td>
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<td></td>
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<p><a href="cpp-ranges-elements_view-begin.html"><code>elements_view::begin</code></a> 的返回类型，及 <a href="cpp-ranges-elements_view-end.html"><code>elements_view::end</code></a> 在底层类型为 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 时的返回类型。</p>
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<p>const 限定重载返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*iterator*/</span><span class="sy1"><</span><span class="kw2">true</span><span class="sy1">></span></span></span> 。非 const 限定重载返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*iterator*/</span><span class="sy1"><</span><span class="kw2">false</span><span class="sy1">></span></span></span> 。</p>
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<p>此类模板的名字（此处示为 <code><i>iterator</i></code> ）是未指定的。</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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<td>成员类型</td>
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<td>定义</td>
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<td><code><i>Base</i></code> <span class="t-mark">(私有)</span></td>
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<td>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">Const</span></span> 为 <code>true</code> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> V</span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">V</span></span> 。名字仅用于阐释</td>
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<td><code>iterator_concept</code></td>
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<td>若 <code><i>Base</i></code> 实现 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::random_access_iterator_tag</a></span> ，<br />
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若 <code><i>Base</i></code> 实现 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::bidirectional_iterator_tag</a></span> ，<br />
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若 <code><i>Base</i></code> 实现 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::forward_iterator_tag</a></span> ，<br />
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否则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::input_iterator_tag</a></span></td>
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<tr class="t-dsc">
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<td><code>iterator_category</code></td>
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<td>若 <code><i>Base</i></code> 不实现 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则不定义。
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<ul>
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<li>否则若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std​<span class="sy4">::</span>​get<span class="sy1"><</span>N<span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span>current_<span class="br0">)</span></span></span> 为右值则该类型为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::input_iterator_tag</a></span> 。</li>
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<li>否则令 <code>C</code> 为类型 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>Base<span class="sy1">>></span>​<span class="sy4">::</span>​iterator_category</span></span> 。则若 <code>C</code> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">derived_from</span><span class="sy1"><</span><a href="cpp-iterator-iterator_tags.html"><span class="kw656">std::<span class="me2">random_access_iterator_tag</span></span></a><span class="sy1">></span></span></span> 则该类型为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::random_access_iterator_tag</a></span> 。</li>
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<li>否则该类型为 <code>C</code> 。</li>
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</ul>
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</td>
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<tr class="t-dsc">
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<td><code>value_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span><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, ranges<span class="sy4">::</span><span class="me2">range_value_t</span><span class="sy1"><</span>Base<span class="sy1">>>></span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>difference_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1"><</span>Base<span class="sy1">></span></span></span></td>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.AF.B9.E8.B1.A1">成员对象</span></h3>
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<table class="t-dsc-begin">
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<td>成员名</td>
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<td>定义</td>
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<tr class="t-dsc">
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<td><code><i>current_</i></code> <span class="t-mark">(私有)</span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>Base<span class="sy1">></span></span></span> 类型对象，名字仅用于阐释</td>
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</tr>
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</table>
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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-iterator-iterator.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>构造迭代器<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-iterator-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>返回底层迭代器<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-iterator-operator*.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>访问第 <code>N</code> 元组元素<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-iterator-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>按下标访问元素<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-iterator-operator_arith.html"><span class="t-lines"><span>operator++</span><span>operator++<span style="font-size:0.7em; line-height:130%">(int)</span></span> <span>operator--</span><span>operator--<span style="font-size:0.7em; line-height:130%">(int)</span></span><span>operator+=</span><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>推进或减少底层迭代器<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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</table>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</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-elements_view-iterator-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator<</span><span>operator></span><span>operator<=</span><span>operator>=</span><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>比较底层迭代器<br />
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<span class="t-mark">(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-iterator-operator_arith2.html"><span class="t-lines"><span>operator+</span><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>进行迭代器算术<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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</table>
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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/P2259R1">P2259R1</a></td>
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<td>C++20</td>
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<td>始终定义成员 <code>iterator_category</code></td>
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<td>仅若 <code><i>Base</i></code> 实现 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 才定义</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/issue3555">LWG 3555</a></td>
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<td>C++20</td>
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<td><code>iterator_concept</code> 的定义忽略 const</td>
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<td>使之考虑</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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<td></td>
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<div class="visualClear"></div>
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