99 lines
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99 lines
11 KiB
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<title>std::indirectly_copyable_storable</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_iterator_indirectly_copyable_storable 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>indirectly_copyable_storable</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-iterator.html">iterator</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-iterator.html"><iterator></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> In, <span class="kw1">class</span> Out<span class="sy1">></span><br /></span>
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<p>concept indirectly_copyable_storable <span class="sy1">=</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_copyable</span><span class="sy1"><</span>In, Out<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>Out, std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>Out, <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>Out, std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span><span class="sy3">&&</span><span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>Out, <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span><span class="sy3">&&</span><span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">copyable</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">>></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span>, std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>In<span class="sy1">>></span> <span class="sy3">&&</span><br /></p>
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std<span class="sy4">::</span><span class="me2">assignable_from</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span><span class="sy3">&</span>, std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>In<span class="sy1">>></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>indirectly_copyable_storable</code> 概念指定 <a href="cpp-iterator-indirectly_readable.html"><code>indirectly_readable</code></a> 与 <a href="cpp-iterator-indirectly_writable.html"><code>indirectly_writable</code></a> 类型间的关系。在 <a href="cpp-iterator-indirectly_writable.html"><code>indirectly_writable</code></a> type. In addition to <a href="cpp-iterator-indirectly_copyable.html"><code>indirectly_copyable</code></a> 之外，此概念还指定从 <code>indirectly_readable</code> 类型的复制能通过中间对象进行。</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><code>In</code> 与 <code>Out</code> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">indirectly_copyable_storable</span><span class="sy1"><</span>In, Out<span class="sy1">></span></span></span> ，仅若给定 <code>In</code> 类型的可解引用值 <code>i</code> ：</p>
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<li>在定义 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>In<span class="sy1">></span> obj<span class="br0">(</span><span class="sy2">*</span>i<span class="br0">)</span><span class="sy4">;</span></span></span> 后， <code>obj</code> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>i</span></span> 先前代表的值，而</li>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>In<span class="sy1">></span></span></span> 是右值引用类型，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>i</span></span> 在 <code>obj</code> 的初始化后被置于合法但未指定的状态。</li>
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<h3><span class="mw-headline" id=".E7.9B.B8.E7.AD.89.E6.80.A7.E4.BF.9D.E6.8C.81">相等性保持</span></h3>
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<p>若表达式对给定的相等输入产生相等输出，则它<i>保持相等性</i>。</p>
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<li>表达式的输入由其操作数组成。</li>
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<li>表达式的输出由其结果和表达式所修改的所有操作数（若存在）组成。</li>
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</ul>
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<p>在标准概念的规范中，操作数定义为仅包含下列内容的最大子表达式：</p>
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<li><a href="cpp-language-expressions.html#.E5.88.9D.E7.AD.89.E8.A1.A8.E8.BE.BE.E5.BC.8F">标识表达式</a>，及</li>
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<li>对 <a href="cpp-utility-move.html"><tt>std::move</tt></a> 、 <span class="t-lc"><a href="cpp-utility-forward.html">std::forward</a></span> 与 <span class="t-lc"><a href="cpp-utility-declval.html">std::declval</a></span> 的调用。</li>
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<p>每个操作数的 cv 限定与值类别，是通过假设每个模板类型形参代表一个 cv 无限定的非数组对象类型确定的。</p>
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<p>进一步要求每个要求保持相等性的表达式都<i>稳定</i>：这种表达式带相同输入对象的二次求值必须拥有相等的输出，而无任何对这些输入对象的显式中间修改。</p>
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<p>除非另外提醒，每个用于 <i>requires 表达式</i>中的表达式都要求保持相等性且稳定，而表达式的求值必须只修改其非常操作数。必须不修改常操作数。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div><a href="cpp-iterator-indirectly_copyable.html"><span class="t-lines"><span>indirectly_copyable</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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<td>指定可从 <a href="cpp-iterator-indirectly_readable.html"><code>indirectly_readable</code></a> 类型复制值给 <a href="cpp-iterator-indirectly_writable.html"><code>indirectly_writable</code></a> 类型<br />
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<span class="t-mark">(概念)</span></td>
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<div><a href="cpp-iterator-indirectly_movable_storable.html"><span class="t-lines"><span>indirectly_movable_storable</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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<td>指定可从 <a href="cpp-iterator-indirectly_readable.html"><code>indirectly_readable</code></a> 类型移动值给 <a href="cpp-iterator-indirectly_writable.html"><code>indirectly_writable</code></a> 类型，且该移动可以通过中间对象进行<br />
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<span class="t-mark">(概念)</span></td>
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