131 lines
11 KiB
HTML
131 lines
11 KiB
HTML
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<title>std::incrementable_traits</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_iterator_incrementable_traits 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>incrementable_traits</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-iterator.html">iterator</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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<table class="t-dcl-begin">
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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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<td></td>
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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> <span class="kw1">class</span> I <span class="sy1">></span><br />
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<span class="kw1">struct</span> incrementable_traits <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span></span></div>
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</td>
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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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</tr>
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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> requires <a href="cpp-types-is_object.html"><span class="kw487">std::<span class="me2">is_object_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><br /></p>
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<span class="kw1">struct</span> incrementable_traits<span class="sy1"><</span>T<span class="sy2">*</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> <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="kw1">struct</span> incrementable_traits<span class="sy1"><</span><span class="kw4">const</span> T<span class="sy1">></span> <span class="sy4">:</span> incrementable_traits<span class="sy1"><</span>T<span class="sy1">></span> <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span></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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<tr class="t-dcl t-since-cxx20">
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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> requires requires <span class="br0">{</span> <span class="kw1">typename</span> T<span class="sy4">::</span><span class="me2">difference_type</span><span class="sy4">;</span> <span class="br0">}</span><br /></p>
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<span class="kw1">struct</span> incrementable_traits<span class="sy1"><</span>T<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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<tr class="t-dcl t-since-cxx20">
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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> requires <span class="br0">(</span><span class="sy3">!</span>requires <span class="br0">{</span> <span class="kw1">typename</span> T<span class="sy4">::</span><span class="me2">difference_type</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span> <span class="sy3">&&</span><br />
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requires<span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&</span> a, <span class="kw4">const</span> T<span class="sy3">&</span> b<span class="br0">)</span> <span class="br0">{</span> <span class="br0">{</span> a <span class="sy2">-</span> b <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">integral</span><span class="sy4">;</span> <span class="br0">}</span><br /></p>
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<span class="kw1">struct</span> incrementable_traits<span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">;</span></div>
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<td>(5)</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>计算类型 <code>I</code> 的关联差类型，若它存在。用户可对程序定义类型特化 <code>incrementable_traits</code> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 初等模板是空 struct 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 对指针的特化。提供等于 <span class="t-lc"><a href="cpp-types-ptrdiff_t.html">std::ptrdiff_t</a></span> 的成员类型 <code>difference_type</code> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 对 const 限定类型的特化。</div>
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<div class="t-li1"><span class="t-li">4)</span> 对定义公开可访问成员类型 <code>difference_type</code> 的类型的特化。提供等于 <code>T::difference_type</code> 的成员类型 <code>difference_type</code> 。</div>
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<div class="t-li1"><span class="t-li">5)</span> 对不定义公开可访问成员类型 <code>difference_type</code> 但支持减法的类型的特化。提供等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-make_signed.html"><span class="kw617">std::<span class="me2">make_signed_t</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> <a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy1">></span></span></span> 的成员类型 <code>difference_type</code> 。隐式表达式变种规则（见后述）应用于表达式 <code>a - b</code> 。</div>
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<h3><span class="mw-headline" id=".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</span></h3>
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<p>使用不修改某 const 左值运算数的表达式的 <i>requires 表达式</i>亦隐式要求该表达式的额外变种对给定运算数接受非 const 左值或（可为 const 的）右值，除非以有区别的语义显式要求这种表达式变种。这些<i>隐式表达式变种</i>必须符合与声明的表达式的相同的语义。不指定实现以何种程度校验变种的语法。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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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=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-weakly_incrementable.html"><span class="t-lines"><span>weakly_incrementable</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>指定 <a href="cpp-concepts-semiregular.html"><code>semiregular</code></a> 类型能以前后自增运算符自增<br />
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<span class="t-mark">(概念)</span></td>
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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-iterator-iter_t.html"><span class="t-lines"><span>iter_value_t</span><span>iter_reference_t</span><span>iter_difference_t</span><span>iter_rvalue_reference_t</span><span>iter_common_reference_t</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><span class="t-mark-rev t-since-cxx20">(C++20)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span><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>计算迭代器的关联类型<br />
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<span class="t-mark">(别名模板)</span></td>
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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-iterator-iterator_traits.html"><span class="t-lines"><span>iterator_traits</span></span></a></div>
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</div>
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<td>为迭代器各项性质提供统一接口<br />
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<span class="t-mark">(类模板)</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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