74 lines
6.7 KiB
HTML
74 lines
6.7 KiB
HTML
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<title>std::experimental::ranges::WeaklyIncrementable</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_experimental_ranges_iterator_WeaklyIncrementable 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::experimental::ranges::</span>WeaklyIncrementable</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a>‎ | <a href="cpp-experimental-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-experimental-ranges-iterator.html"><experimental/ranges/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> I<span class="sy1">></span><br /></span>
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<p>concept <span class="kw4">bool</span> WeaklyIncrementable <span class="sy1">=</span><br />
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<a href="cpp-experimental-ranges-concepts-Semiregular.html"><span class="kw2554">ranges::<span class="me2">Semiregular</span></span></a><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
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requires<span class="br0">(</span>I i<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">typename</span> ranges<span class="sy4">::</span><span class="me2">difference_type_t</span><span class="sy1"><</span>I<span class="sy1">></span><span class="sy4">;</span><br />
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requires <a href="cpp-experimental-ranges-concepts-SignedIntegral.html"><span class="kw2536">ranges::<span class="me2">SignedIntegral</span></span></a><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">difference_type_t</span><span class="sy1"><</span>I<span class="sy1">>></span><span class="sy4">;</span><br />
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<span class="br0">{</span> <span class="sy2">++</span>i <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> <a href="cpp-experimental-ranges-concepts-Same.html"><span class="kw2530">ranges::<span class="me2">Same</span></span></a><span class="sy1"><</span>I<span class="sy1">></span><span class="sy3">&</span><span class="sy4">;</span> <span class="coMULTI">/* 不要求保持相等性 */</span><br />
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i<span class="sy2">++</span><span class="sy4">;</span> <span class="coMULTI">/* 不要求保持相等性 */</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-ranges-ts t-mark-ts">(范围 TS)</span></td>
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<p>概念 <code>WeaklyIncrementable<I></code> 指定能（以前和后自增运算符）自增的类型上的要求。自增运算不需要保持相等性，而且类型不必为 <a href="cpp-experimental-ranges-concepts-EqualityComparable.html"><code>EqualityComparable</code></a> 。</p>
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<p>令 <code>i</code> 为 <code>I</code> 类型对象。若 <code>i</code> 在前和后自增的定义域中，则说它<i>可自增</i>。 <code>WeaklyIncrementable<I></code> 仅若下列条件成立才得到满足：</p>
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<ul>
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<li><code>++i</code> 与 <code>i++</code> 有相同的定义域；</li>
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<li>若 <code>i</code> 可自增，则：
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<li><code>++i</code> 与 <code>i++</code> 均令 <code>i</code> 前进到下个元素；且</li>
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<li><code>++i</code> 与 <code>i</code> 指代同一对象。</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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<ul>
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<li>表达式的输入由其运算数组成。</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运算数（若存在）组成。</li>
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</ul>
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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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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>对于 <code>WeaklyIncrementable</code> 类型， <code>a</code> 等于 <code>b</code> 不蕴含 <code>++a</code> 等于 <code>++b</code> 。在这种类型上的算法应该为单趟，且决不试图二次经过相同值。</p>
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