103 lines
6.6 KiB
HTML
103 lines
6.6 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::coroutine_traits</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_coroutine_coroutine_traits skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>coroutine_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-coroutine.html">coroutine</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-coroutine.html"><coroutine></a></code></div>
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</td>
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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> R, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">struct</span> coroutine_traits<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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<p>从协程的返回类型与形参类型确定承诺类型。标准库实现提供与 <code>R::promise_type</code> 相同的公开可访问成员类型 <code>promise_type</code> ，若该有限定标识合法并代表类型。否则它无成员。</p>
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<p><code>coroutine_traits</code> 的程序定义特化应当定义公开可访问的成员类型 <code>promise_type</code> ，否则行为未定义。</p>
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<h3><span class="mw-headline" id=".E6.A8.A1.E6.9D.BF.E5.BD.A2.E5.8F.82">模板形参</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>R</td>
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<td>-</td>
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<td>协程的返回类型</td>
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</tr>
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<tr class="t-par">
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<td>Args</td>
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<td>-</td>
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<td>协程的形参类型，若协程为非静态成员函数则包括<a href="cpp-language-member_functions.html#.E5.BC.95.E7.94.A8.E9.99.90.E5.AE.9A.E7.9A.84.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">隐式对象形参</a></td>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>类型</td>
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<td>定义</td>
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</tr>
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<tr class="t-dsc">
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<td><code>promise_type</code></td>
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<td><code>R::promise_type</code> ，若它合法，或由程序定义特化提供</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span>, <span class="kw1">class</span>...<span class="sy1">></span>
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<span class="kw1">struct</span> coroutine_traits <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> R, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
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requires requires <span class="br0">{</span> <span class="kw1">typename</span> R<span class="sy4">::</span><span class="me2">promise_type</span> <span class="br0">}</span>
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<span class="kw1">struct</span> coroutine_traits<span class="sy1"><</span>R, Args...<span class="sy1">></span> <span class="br0">{</span>
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<span class="kw1">using</span> promise_type <span class="sy1">=</span> R<span class="sy4">::</span><span class="me2">promise_type</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span></pre></div>
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</div>
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</td>
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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>若协程为非静态成员函数，则 <code>Args...</code> 中的首个类型为隐式对象形参的类型，而剩下的是函数的形参类型（若存在）。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">coroutind_traits</span><span class="sy1"><</span>R, Args...<span class="sy1">></span><span class="sy4">::</span><span class="me2">promise_type</span></span></span> 不存在或不是类类型，则对应的协程定义为谬构。</p>
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<p>用户可定义取决于程序定义类型的 <code>coroutine_traits</code> 显式或偏特化，以避免修改返回类型。</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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</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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</html>
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