146 lines
19 KiB
HTML
146 lines
19 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>std::ranges::subrange<I,S,K>::operator PairLike</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_subrange_operator_PairLike skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::subrange<I,S,K>::</span>operator PairLike</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</a>‎ | <a href="cpp-ranges-subrange.html">subrange</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="coMULTI">/*different-from*/</span><span class="sy1"><</span>subrange<span class="sy1">></span> PairLike <span class="sy1">></span><br /></span>
|
|
<p> requires <span class="coMULTI">/*pair-like-convertible-from*/</span><span class="sy1"><</span>PairLike, <span class="kw4">const</span> I<span class="sy3">&</span>, <span class="kw4">const</span> S<span class="sy3">&</span><span class="sy1">></span><br /></p>
|
|
<span class="kw4">constexpr</span> operator PairLike<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl-h">
|
|
<td>
|
|
<div>辅助概念</div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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>
|
|
<p>concept <span class="coMULTI">/*pair-like*/</span> <span class="sy1">=</span> <span class="co1">// 仅用于阐释</span><br />
|
|
<span class="sy3">!</span><a href="cpp-types-is_reference.html"><span class="kw481">std::<span class="me2">is_reference_v</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span> requires<span class="br0">(</span>T t<span class="br0">)</span> <span class="br0">{</span><br />
|
|
<span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_size.html"><span class="kw1101">std::<span class="me2">tuple_size</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span><span class="sy4">;</span> <span class="co1">// 确保 std::tuple_size<T> 完整</span><br />
|
|
requires std<span class="sy4">::</span><span class="me2">derived_from</span><span class="sy1"><</span><a href="cpp-utility-tuple-tuple_size.html"><span class="kw1101">std::<span class="me2">tuple_size</span></span></a><span class="sy1"><</span>T<span class="sy1">></span>,<br />
|
|
<a href="cpp-types-integral_constant.html"><span class="kw647">std::<span class="me2">integral_constant</span></span></a><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a>, <span class="nu0">2</span><span class="sy1">>></span><span class="sy4">;</span><br />
|
|
<span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">0</span>, <a href="cpp-types-remove_cv.html"><span class="kw595">std::<span class="me2">remove_const</span></span></a><span class="sy1"><</span>T<span class="sy1">>></span><span class="sy4">;</span><br />
|
|
<span class="kw1">typename</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, <a href="cpp-types-remove_cv.html"><span class="kw595">std::<span class="me2">remove_const</span></span></a><span class="sy1"><</span>T<span class="sy1">>></span><span class="sy4">;</span><br />
|
|
<span class="br0">{</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>t<span class="br0">)</span> <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span><span class="kw4">const</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">0</span>, T<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span><br />
|
|
<span class="br0">{</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>t<span class="br0">)</span> <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span><span class="kw4">const</span> <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, T<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span><br /></p>
|
|
<span class="br0">}</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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="kw1">class</span> U, <span class="kw1">class</span> V <span class="sy1">></span><br /></span>
|
|
<p>concept <span class="coMULTI">/*pair-like-convertible-from*/</span> <span class="sy1">=</span> <span class="co1">// 仅用于阐释</span><br />
|
|
<span class="sy3">!</span>ranges<span class="sy4">::</span><span class="me2">range</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span> <span class="coMULTI">/*pair-like*/</span><span class="sy1"><</span>T<span class="sy1">></span> <span class="sy3">&&</span><br />
|
|
std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>T, U, V<span class="sy1">></span> <span class="sy3">&&</span><br />
|
|
<span class="coMULTI">/*convertible-to-non-slicing*/</span><span class="sy1"><</span>U, <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">0</span>, T<span class="sy1">>></span> <span class="sy3">&&</span><br /></p>
|
|
std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span>V, <a href="cpp-utility-tuple-tuple_element.html"><span class="kw1100">std::<span class="me2">tuple_element_t</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, T<span class="sy1">>></span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(3)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">1)</span> 转换 <code>subrange</code> 为 pair 式类型（即实现 <code><i>pair-like</i></code> 的类型，见后述）。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> PairLike<span class="br0">(</span>i_, s_<span class="br0">)</span><span class="sy4">;</span></span></span> ，其中 <code>i_</code> 与 <code>s_</code> 分别为存储的迭代器与哨位。此转换函数拥有 <code><i>pair-like-convertible</i></code> （见后述）所施加的额外约束。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 仅用于阐释的概念 <code><i>pair-like</i></code> 指定类型为 pair 式类型。通常而言， pair 式类型的表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 能用于<a href="cpp-language-structured_binding.html">结构化绑定</a>（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> <span class="br0">[</span>x, y<span class="br0">]</span> <span class="sy1">=</span> e<span class="sy4">;</span></span></span> 通常为良构）。同标准概念，此概念得到实现，若它得到满足且其蕴含的所有概念均得到实现。</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 仅用于阐释的概念 <code><i>pair-like-convertible-from</i></code> 细化 <code><i>pair-like</i></code> 。它拒绝 <a href="cpp-ranges-range.html"><code>range</code></a> 类型，并要求 <code>U</code> 与 <code>V</code> 分别可转换成 <code>T</code> 的第一与第二元素类型，并且从 <code>U</code> （将被替换成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> I<span class="sy3">&</span></span></span> ）的转换为非切片（见 <a href="cpp-ranges-subrange-subrange.html"><tt><i>convertible-to-non-slicing</i></tt></a> ）。同标准概念，此概念得到实现，若它得到满足且其蕴含的所有概念均得到实现。</div>
|
|
<p>仅用于阐释的概念 <code><i>different-from</i></code> 为类型 <code>T</code> 与 <code>U</code> 实现，当且仅当 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>U<span class="sy1">></span></span></span> 是不同的类型。</p>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<p>（无）</p>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>从存储的迭代器与哨位直接初始化 <code>PairLike</code> 值。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>下列类型为 pair 式：</p>
|
|
<ul>
|
|
<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span>T, U<span class="sy1">></span></span></span></li>
|
|
<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span>T, U<span class="sy1">></span></span></span></li>
|
|
<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>T, <span class="nu0">2</span><span class="sy1">></span></span></span></li>
|
|
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span><span class="sy1"><</span>I, S, K<span class="sy1">></span></span></span></li>
|
|
</ul>
|
|
<p>从这些类型之一或 <span class="t-lc"><a href="cpp-utility-variant.html">std::variant</a></span> 特化派生的程序定义类型为 pair 式，若</p>
|
|
<ul>
|
|
<li><code>std::tuple_size</code> 与 <code>std::tuple_element</code> 对它正确特化，且</li>
|
|
<li>对其值调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span><span class="nu0">0</span><span class="sy1">></span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1"><</span><span class="nu0">1</span><span class="sy1">></span></span></span> 为良构。</li>
|
|
</ul>
|
|
<p>由于 <code>subrange</code> 特化是 <a href="cpp-ranges-range.html"><code>range</code></a> 类型，到它们的转换不经由此转换函数进行。</p>
|
|
<p><span class="t-lc"><a href="cpp-container-array.html">std::array</a></span> 特化不能从 <code>subrange</code> 转换而来，因为它们是 <a href="cpp-ranges-range.html"><code>range</code></a> 类型。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <ranges></span>
|
|
<span class="co2">#include <string></span>
|
|
<span class="co2">#include <utility></span>
|
|
|
|
<span class="kw1">using</span> legacy_strview <span class="sy1">=</span> <a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span>
|
|
std<span class="sy4">::</span><span class="me2">string</span><span class="sy4">::</span><span class="me2">const_iterator</span>,
|
|
std<span class="sy4">::</span><span class="me2">string</span><span class="sy4">::</span><span class="me2">const_iterator</span>
|
|
<span class="sy1">></span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">void</span> legacy_print<span class="br0">(</span>legacy_strview p<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> p.<span class="me1">first</span> <span class="sy3">!</span><span class="sy1">=</span> p.<span class="me1">second</span><span class="sy4">;</span> <span class="sy2">++</span>p.<span class="me1">first</span><span class="br0">)</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="sy2">*</span>p.<span class="me1">first</span> <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> dat<span class="br0">{</span><span class="st0">"ABCDE"</span><span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> v<span class="br0">{</span> std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span><span class="br0">{</span>dat<span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span> v<span class="sy4">;</span> v <span class="sy1">=</span> <span class="br0">{</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">}</span><span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="coMULTI">/*...*/</span>
|
|
legacy_print<span class="br0">(</span>legacy_strview<span class="br0">{</span>v<span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">A B C D E
|
|
A B C D
|
|
A B C
|
|
A B
|
|
A</pre></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|