115 lines
10 KiB
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115 lines
10 KiB
HTML
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<title>std::ranges::subrange 的推导指引</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_subrange_deduction_guides skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><code>std::ranges::subrange</code> 的推导指引</h1>
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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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_or_output_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S <span class="sy1">></span><br />
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subrange<span class="br0">(</span>I, S<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> subrange<span class="sy1"><</span>I, S<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> std<span class="sy4">::</span><span class="me2">input_or_output_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S <span class="sy1">></span><br /></span>
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<p>subrange<span class="br0">(</span>I, S, <span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>></span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span><br /></p>
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subrange<span class="sy1"><</span>I, S, ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</span><span class="sy1">></span><span class="sy4">;</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> ranges<span class="sy4">::</span><span class="me2">borrowed_range</span><span class="sy1"><</span>R<span class="sy1">></span> <span class="sy1">></span><br /></span>
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<p>subrange<span class="br0">(</span>R<span class="sy3">&&</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span><br />
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subrange<span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>R<span class="sy1">></span>,<br />
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<span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">sized_range</span><span class="sy1"><</span>R<span class="sy1">></span> <span class="sy3">||</span><br />
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std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>,<br />
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ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>R<span class="sy1">>></span><span class="br0">)</span> <span class="sy4">?</span><br /></p>
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ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</span> <span class="sy4">:</span> ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">unsized</span><span class="sy1">></span><span class="sy4">;</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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<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">borrowed_range</span><span class="sy1"><</span>R<span class="sy1">></span> <span class="sy1">></span><br /></span>
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<p>subrange<span class="br0">(</span>R<span class="sy3">&&</span>, <span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1"><</span>R<span class="sy1">>></span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span><br />
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subrange<span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>R<span class="sy1">></span>,<br /></p>
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ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</span><span class="sy1">></span><span class="sy4">;</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>为 <span class="t-lc">std::ranges::subrange</span> 提供这些<a href="cpp-language-class_template_argument_deduction.html">推导指引</a>。</p>
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<div class="t-li1"><span class="t-li">1)</span> 从迭代器与哨位类型推导模板实参。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>S, I<span class="sy1">></span></span></span> 得以满足则 <code>subrange</code> 为有大小，如默认模板实参所确定。</div>
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<div class="t-li1"><span class="t-li">2)</span> 在指定范围大小时从迭代器与哨位类型推导模板实参。 <code>subrange</code> 始终为有大小。</div>
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<div class="t-li1"><span class="t-li">3)</span> 从范围类型推导模板实参。若能从范围或其迭代器与哨位获得大小则 <code>subrange</code> 有大小。</div>
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<div class="t-li1"><span class="t-li">4)</span> 在指定范围大小时从范围类型推导模板实参。 <code>subrange</code> 始终为有大小。</div>
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<p>仅用于阐释的别名模板 <code><i>make-unsigned-like-t</i></code> 将每个<a href="cpp-iterator-weakly_incrementable.html#.E6.95.B4.E6.95.B0.E5.BC.8F.E7.B1.BB.E5.9E.8B">整数式类型</a>映射到其对应的无符号版本。</p>
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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>在构造 <code>subrange</code> 对象时，</p>
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<ul>
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<li>对于 <span class="t-v">(1,2)</span> ，若迭代器-哨位对不代表合法范围则行为未定义，</li>
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<li>对于 <span class="t-v">(2,4)</span> ，若给定的大小不等于范围大小则行为未定义。</li>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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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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<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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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3404">LWG 3404</a></td>
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<td>C++20</td>
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<td>提供了无意义的来自 pair 式类型的推导指引</td>
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<td>已移除</td>
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