59 lines
6.2 KiB
HTML
59 lines
6.2 KiB
HTML
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<title>std::ranges::range</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_range 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::</span>range</h1>
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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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span><br /></span>
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<p>concept range <span class="sy1">=</span> requires<span class="br0">(</span>T<span class="sy3">&</span> t<span class="br0">)</span> <span class="br0">{</span><br />
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ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>t<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 对向前迭代器保持相等性</span><br />
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ranges<span class="sy4">::</span><span class="me2">end</span> <span class="br0">(</span>t<span class="br0">)</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><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p><code>range</code> 概念定义允许通过指代元素范围的迭代器和哨位，在其元素上迭代的类型。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E4.B9.89.E8.A6.81.E6.B1.82">语义要求</span></h3>
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<p>给定满足 <span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span><span class="br0">(</span>E<span class="br0">)</span><span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">T</span></span> 的表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E</span></span> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">T</span></span> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">range</span></span> 仅若：</p>
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<ul>
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<li>[<span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>E<span class="br0">)</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>E<span class="br0">)</span></span></span>) 代表范围，且</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>E<span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>E<span class="br0">)</span></span></span> 均有均摊常量时间复杂度且不会以对于保持相等性的表达式可观察的方式更改 <span class="t-c"><span class="mw-geshi cpp source-cpp">E</span></span> 的值，且</li>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>E<span class="br0">)</span></span></span> 的类型实现 <a href="cpp-iterator-forward_iterator.html"><code>forward_iterator</code></a> ，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>E<span class="br0">)</span></span></span> 保持相等性（换言之，向前迭代器支持多趟算法）</li>
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<p>注意：在上述定义中，要求的表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span></span></span> 不要求<a href="cpp-concepts-equality_comparable.html#.E9.9A.90.E5.BC.8F.E8.A1.A8.E8.BE.BE.E5.BC.8F.E5.8F.98.E7.A7.8D">隐式表达式变种</a>。</p>
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