88 lines
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88 lines
16 KiB
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::ranges::</span>RandomAccessIterator</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> RandomAccessIterator <span class="sy1">=</span><br />
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<a href="cpp-experimental-ranges-iterator-BidirectionalIterator.html"><span class="kw2572">ranges::<span class="me2">BidirectionalIterator</span></span></a><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
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<a href="cpp-experimental-ranges-concepts-DerivedFrom.html"><span class="kw2531">ranges::<span class="me2">DerivedFrom</span></span></a><span class="sy1"><</span><br />
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ranges<span class="sy4">::</span><span class="me2">iterator_category_t</span><span class="sy1"><</span>I<span class="sy1">></span>, ranges<span class="sy4">::</span><span class="me2">random_access_iterator_tag</span><br />
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<span class="sy1">></span> <span class="sy3">&&</span><br />
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<a href="cpp-experimental-ranges-concepts-StrictTotallyOrdered.html"><span class="kw2545">ranges::<span class="me2">StrictTotallyOrdered</span></span></a><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
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<a href="cpp-experimental-ranges-iterator-SizedSentinel.html"><span class="kw2568">ranges::<span class="me2">SizedSentinel</span></span></a><span class="sy1"><</span>I, I<span class="sy1">></span> <span class="sy3">&&</span><br />
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requires<span class="br0">(</span>I i, <span class="kw4">const</span> I j, <span class="kw4">const</span> ranges<span class="sy4">::</span><span class="me2">difference_type_t</span><span class="sy1"><</span>I<span class="sy1">></span> n<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="br0">{</span> i <span class="sy2">+</span><span class="sy1">=</span> n <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><br />
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<span class="br0">{</span> j <span class="sy2">+</span> n <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><br />
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<span class="br0">{</span> n <span class="sy2">+</span> j <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><br />
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<span class="br0">{</span> i <span class="sy2">-</span><span class="sy1">=</span> n <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><br />
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<span class="br0">{</span> j <span class="sy2">-</span> n <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><br />
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j<span class="br0">[</span>n<span class="br0">]</span><span class="sy4">;</span><br />
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requires <a href="cpp-experimental-ranges-concepts-Same.html"><span class="kw2530">ranges::<span class="me2">Same</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>j<span class="br0">[</span>n<span class="br0">]</span><span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">reference_t</span><span class="sy1"><</span>I<span class="sy1">>></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-ranges-ts t-mark-ts">(范围 TS)</span></td>
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<p>概念 <code>RandomAccessIterator<I></code> 细化 <a href="cpp-experimental-ranges-iterator-BidirectionalIterator.html"><code>BidirectionalIterator</code></a> ，添加用 <code>+=</code> 、 <code>-=</code> 、 <code>+</code> 和 <code>-</code> 运算符的常数时间前进、用 <code>-</code> 的常数时间距离计算，及带下标的数组记法支持。</p>
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<p>令 <code>a</code> 与 <code>b</code> 为 <code>I</code> 类型的合法迭代器，使得从 <code>a</code> 可抵达 <code>b</code> ，并令 <code>n</code> 为等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">b <span class="sy2">-</span> a</span></span> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">difference_type_t</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 类型值。 <code>RandomAccessIterator<I></code> 仅若符合下列条件才得到满足：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">b</span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>a <span class="sy2">+</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>a<span class="br0">)</span></span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>n <span class="sy2">+</span> a<span class="br0">)</span></span></span> 。</li>
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<li>对于任何二个正整数 <code>x</code> 与 <code>y</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">+</span> <span class="br0">(</span>x <span class="sy2">+</span> y<span class="br0">)</span></span></span> 合法，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">+</span> <span class="br0">(</span>x <span class="sy2">+</span> y<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span> x<span class="br0">)</span> <span class="sy2">+</span> y</span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">+</span> <span class="nu0">0</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">a</span></span> 。</li>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span> <span class="br0">(</span>n <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span></span></span> 合法，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">--</span>b</span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy2">+</span> <span class="br0">(</span>n <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>b <span class="sy2">+</span><span class="sy1">=</span> <span class="sy2">-</span>n<span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>b <span class="sy2">-</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 都等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">a</span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>b <span class="sy2">-</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>b<span class="br0">)</span></span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>b <span class="sy2">-</span> n<span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>b <span class="sy2">-</span><span class="sy1">=</span> n<span class="br0">)</span></span></span> 。</li>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">b</span></span> 可解引用，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>n<span class="br0">]</span></span></span> 合法并等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>b</span></span> 。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span><span class="br0">(</span>a <span class="sy1"><=</span> b<span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</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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<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运算数。必须不修改常运算数。</p>
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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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