423 lines
36 KiB
HTML
423 lines
36 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::ranges::views::single, std::ranges::single_view</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_single_view 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><span style="font-size:0.7em; line-height:130%">views::</span>single, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>single_view</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-ranges.html">ranges</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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<td>
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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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</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> std<span class="sy4">::</span><span class="me2">copy_constructible</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">class</span> single_view <span class="sy4">:</span> <span class="kw1">public</span> ranges<span class="sy4">::</span><span class="me2">view_interface</span><span class="sy1"><</span>single_view<span class="sy1"><</span>T<span class="sy1">>></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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">namespace</span> views <span class="br0">{</span><br /></span>
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<p> <span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/*unspecified*/</span> single <span class="sy1">=</span> <span class="coMULTI">/*unspecified*/</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</span></div>
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</td>
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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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<td></td>
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<div class="t-li1"><span class="t-li">1)</span> 产生准确含有一个拥有指定值元素的 <a href="cpp-ranges-view.html"><code>view</code></a> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">single</span><span class="br0">(</span>e<span class="br0">)</span></span></span> 对任何适合的子表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于 <span class="t-c"><span class="mw-geshi cpp source-cpp">single_view<span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span><span class="br0">(</span>e<span class="br0">)</span><span class="br0">)</span><span class="sy1">>></span><span class="br0">(</span>e<span class="br0">)</span></span></span> 。</div>
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<p><code>single_view</code> 的典型实现存储一个 <code><a href="cpp-ranges-copyable_wrapper.html"><i>copyable-box</i></a><T></code> 类型成员。为描述目的，下面称该成员为 <code>value_</code> 。</p>
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<p>元素的生存期绑定到所属的 <code>single_view</code> 。复制 <code>single_view</code> 会进行元素的复制。</p>
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<h3><span class="mw-headline" id=".E8.A1.A8.E8.BE.BE.E5.BC.8F.E7.AD.89.E4.BB.B7">表达式等价</span></h3>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 拥有相同效果，均为<a href="cpp-language-noexcept_spec.html">潜在抛出</a>或均非潜在抛出（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>e<span class="br0">)</span> <span class="sy1">==</span> <span class="kw1">noexcept</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ），且均为<a href="cpp-language-constant_expression.html">常量子表达式</a>或均非常量子表达式。</p>
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<h3><span class="mw-headline" id=".E5.AE.9A.E5.88.B6.E7.82.B9.E5.AF.B9.E8.B1.A1">定制点对象</span></h3>
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<p>名字 <code>views::single</code> 代表一个<i>定制点对象</i>，它是<a href="cpp-named_req-LiteralType.html">字面</a> <a href="cpp-concepts-semiregular.html"><code>semiregular</code></a> 类类型的 const <a href="cpp-named_req-FunctionObject.html">函数对象</a>。为说明目的，以 <code><i>__single_fn</i></code> 表示其类型的 cv 无限定版本。</p>
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<p><code><i>__single_fn</i></code> 的所有实例均相等。在相同参数上调用类型 <code><i>__single_fn</i></code> 的不同实例的效果是等价的，无关乎指代该实例的表达式是左值还是右值，以及是否为 const 限定（然而不要求 volatile 限定的实例可调用）。从而能自由地复制 <code>views::single</code> 并且能彼此替代地使用其副本。</p>
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<p>给定类型集合 <code>Args...</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>...</span></span> 满足上面对于 <code>views::single</code> 的参数要求，则 <code><i>__single_fn</i></code> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__single_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __single_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__single_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __single_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 。否则， <code><i>__single_fn</i></code> 的函数调用运算符不参与重载决议。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><strong class="selflink"><span class="t-lines"><span>(构造函数)</span></span></strong></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>构造 <code>single_view</code><br />
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<span class="t-mark">(公开成员函数)</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><strong class="selflink"><span class="t-lines"><span>begin</span></span></strong></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>返回指向元素的指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><strong class="selflink"><span class="t-lines"><span>end</span></span></strong></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>返回元素后一位置的指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><strong class="selflink"><span class="t-lines"><span>size</span></span></strong></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span> <span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</td>
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<td>返回 1 （一）<br />
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<span class="t-mark">(公开静态成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><strong class="selflink"><span class="t-lines"><span>data</span></span></strong></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>返回指向元素的指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::ranges::view_interface">继承自 <span class="t-lc">std::ranges::view_interface</span></span></h5>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-empty.html"><span class="t-lines"><span>empty</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>返回视图是否为空。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-operator_bool.html"><span class="t-lines"><span>operator bool</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>返回派生视图是否为非空。若 <span class="t-lc">ranges::empty</span> 可应用于它则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-front.html"><span class="t-lines"><span>front</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>返回派生视图中的首元素。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-back.html"><span class="t-lines"><span>back</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>返回派生视图中的末元素。若视图满足 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 与 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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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-ranges-view_interface-operator_at.html"><span class="t-lines"><span>operator[]</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>返回派生视图中的第 n 个元素。若视图满足 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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</table>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::single_view::single_view"><span style="font-size:0.7em; line-height:130%">std::ranges::single_view::</span>single_view</span></h2>
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<div><span class="mw-geshi cpp source-cpp">single_view<span class="br0">(</span><span class="br0">)</span> requires std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy1">=</span> <span class="kw1">default</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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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw1">explicit</span> single_view<span class="br0">(</span> <span class="kw4">const</span> T<span class="sy3">&</span> t <span class="br0">)</span><span class="sy4">;</span></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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</tr>
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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="kw4">constexpr</span> <span class="kw1">explicit</span> single_view<span class="br0">(</span> T<span class="sy3">&&</span> t <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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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>
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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>... <span class="me1">Args</span> <span class="sy1">></span><br /></span>
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<p> requires std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>T, Args...<span class="sy1">></span><br /></p>
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<span class="kw4">constexpr</span> <span class="kw1">explicit</span> single_view<span class="br0">(</span> <a href="cpp-utility-in_place.html"><span class="kw1082">std::<span class="me2">in_place_t</span></span></a>, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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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>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<p>构造 <code>single_view</code> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认初始化 <code>value_</code> ，值初始化其所含的值。</div>
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<div class="t-li1"><span class="t-li">2)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp">t</span></span> 初始化 <code>value_</code> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>t<span class="br0">)</span></span></span> 初始化 <code>value_</code> 。</div>
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<div class="t-li1"><span class="t-li">4)</span> 如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">value_<span class="br0">{</span><a href="cpp-utility-in_place.html"><span class="kw1081">std::<span class="me2">in_place</span></span></a>, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">}</span></span></span> 初始化 <code>value_</code> 。</div>
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</div>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::single_view::begin"><span style="font-size:0.7em; line-height:130%">std::ranges::single_view::</span>begin</span></h2>
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<table class="t-dcl-begin">
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> T<span class="sy2">*</span> begin<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span><br />
|
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<span class="kw4">constexpr</span> <span class="kw4">const</span> T<span class="sy2">*</span> begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> data<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></span> 。</p>
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</div>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::single_view::end"><span style="font-size:0.7em; line-height:130%">std::ranges::single_view::</span>end</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> T<span class="sy2">*</span> end<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span><br />
|
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<span class="kw4">constexpr</span> <span class="kw4">const</span> T<span class="sy2">*</span> end<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> data<span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> <span class="nu0">1</span><span class="sy4">;</span></span></span> 。</p>
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</div>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::single_view::size"><span style="font-size:0.7em; line-height:130%">std::ranges::single_view::</span>size</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span> <span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> size<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span></span></span> 。</p>
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<p>此为静态函数。这使得 <code>single_view</code> 实现 <a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/ranges/split_view&action=edit&redlink=1" class="new" title="cpp/ranges/split view（页面不存在）"><code>split_view</code></a> 所要求的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*tiny-range*/</span></span></span> 。</p>
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</div>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::single_view::data"><span style="font-size:0.7em; line-height:130%">std::ranges::single_view::</span>data</span></h2>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> T<span class="sy2">*</span> data<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span><br />
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<span class="kw4">constexpr</span> <span class="kw4">const</span> T<span class="sy2">*</span> data<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>返回指向 <code>value_</code> 的所含值的指针。若 <code>value_</code> 不含值则行为未定义。</p>
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</div>
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<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95">推导指引</span></h3>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<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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single_view<span class="br0">(</span>T<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> single_view<span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>对于一个 <code>single_view</code> ，继承的 <code>empty</code> 成员函数始终返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，而继承的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="kw4">bool</span></span></span> 转换函数始终返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</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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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <ranges></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <tuple></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">single_view</span> sv1<span class="br0">{</span><span class="nu16">3.1415</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 使用 (const T&) 构造函数</span>
|
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static_assert<span class="br0">(</span>sv1<span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span>not sv1.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"1) *sv1.data(): "</span> <span class="sy1"><<</span> <span class="sy2">*</span>sv1.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"2) *sv1.begin(): "</span> <span class="sy1"><<</span> <span class="sy2">*</span>sv1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"3) sv1.size(): "</span> <span class="sy1"><<</span> sv1.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"4) distance: "</span> <span class="sy1"><<</span> <a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>sv1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, sv1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> str<span class="br0">{</span><span class="st0">"C++20"</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"5) str = "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-quoted.html"><span class="kw1802">std::<span class="me2">quoted</span></span></a><span class="br0">(</span>str<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">single_view</span> sv2<span class="br0">{</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>str<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 使用 (T&&) 构造函数</span>
|
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"6) *sv2.data(): "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-quoted.html"><span class="kw1802">std::<span class="me2">quoted</span></span></a><span class="br0">(</span><span class="sy2">*</span>sv2.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
|
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<span class="sy1"><<</span> <span class="st0">"7) str = "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-quoted.html"><span class="kw1802">std::<span class="me2">quoted</span></span></a><span class="br0">(</span>str<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">single_view</span><span class="sy1"><</span><a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">double</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">>></span>
|
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sv3<span class="br0">{</span><a href="cpp-utility-in_place.html"><span class="kw1081">std::<span class="me2">in_place</span></span></a>, <span class="nu0">42</span>, <span class="nu16">3.14</span>, <span class="st0">"😄"</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// uses (std::in_place_t, Args&&... args)</span>
|
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"8) sv3 holds a tuple: { "</span>
|
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<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span><span class="nu0">0</span><span class="sy1">></span><span class="br0">(</span>sv3<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">", "</span>
|
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<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span><span class="nu0">1</span><span class="sy1">></span><span class="br0">(</span>sv3<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">", "</span>
|
|
<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span><span class="nu0">2</span><span class="sy1">></span><span class="br0">(</span>sv3<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" }<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
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</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">1) *sv1.data(): 3.1415
|
|
2) *sv1.begin(): 3.1415
|
|
3) sv1.size(): 1
|
|
4) distance: 1
|
|
5) str = "C++20"
|
|
6) *sv2.data(): "C++20"
|
|
7) str = ""
|
|
8) sv3 holds a tuple: { 42, 3.14, 😄 }</pre></div>
|
|
</div>
|
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</div>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<th>正确行为</th>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3428">LWG 3428</a></td>
|
|
<td>C++20</td>
|
|
<td><code>single_view</code> 可从 <span class="t-lc"><a href="cpp-utility-in_place.html">std::in_place_t</a></span> 转换</td>
|
|
<td>使该构造函数为 explicit</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.link/P2367R0">P2367R0</a></td>
|
|
<td>C++20</td>
|
|
<td><code>single_view</code> 的推导指引无法衰变参数；<br />
|
|
<code>views::single</code> 复制但不包装 <code>single_view</code></td>
|
|
<td>提供衰变的推导指引；<br />
|
|
使之始终包装</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-ranges-empty_view.html"><span class="t-lines"><span>ranges::empty_view</span><span>views::empty</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>无元素的空 <a href="cpp-ranges-view.html"><code>view</code></a><br />
|
|
<span class="t-mark">(类模板)</span> <span class="t-mark">(变量模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/ranges/split_view&action=edit&redlink=1" class="new" title="cpp/ranges/split view（页面不存在）"><span class="t-lines"><span>ranges::split_view</span><span>views::split</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>用某个分隔符切割另一 <a href="cpp-ranges-view.html"><code>view</code></a> 所获得的子范围的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
|
|
<span class="t-mark">(类模板)</span> <span class="t-mark">(范围适配器对象)</span></td>
|
|
</tr>
|
|
</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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</html>
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