81 lines
9.6 KiB
HTML
81 lines
9.6 KiB
HTML
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<title>std::experimental::future<T>::then</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::future<T>::</span>then</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-future.html">future</a></span></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> F <span class="sy1">></span><br />
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future<span class="sy1"><</span><span class="coMULTI">/* see below */</span><span class="sy1">></span> then<span class="br0">(</span>F<span class="sy3">&&</span> func<span class="br0">)</span> <span class="sy4">;</span></span></div>
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<p>附着持续 <code>func</code> 到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 。若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 无关联共享状态（即 <span class="t-c"><span class="mw-geshi cpp source-cpp">valid<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="kw2">false</span></span></span> ）则行为未定义。</p>
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<p>创建与要返回的 <code>future</code> 对象关联的共享状态，和如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp">DECAY_COPY<span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>func<span class="br0">)</span><span class="br0">)</span></span></span> 构造，在调用 <code>then</code> 的线程中求值的 <code>func</code> 的副本 <span class="t-c"><span class="mw-geshi cpp source-cpp">fd</span></span> ，其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">DECAY_COPY</span></span> 定义为</p>
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<pre class="de1"><span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span>
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<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> DECAY_COPY<span class="br0">(</span>T<span class="sy3">&&</span> v<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>v<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<p>当前与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 关联的共享状态就绪时，在未指定的执行线程上调用<i>持续</i> <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>fd<span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="br0">)</span></span></span> ，其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE</span></span> 是 <a href="cpp-named_req-Callable.html"><span style="font-style:italic">可调用</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Callable)</span></a> 中定义的操作。若该表达式非法，则行为未定义。</p>
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<p>将从持续返回的任何值存储为返回的 <code>future</code> 对象的共享状态中的结果。将任何从持续的执行传播的异常存储为返回的 <code>future</code> 对象的共享状态中的异常结果。</p>
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<p>令 <code>U</code> 为持续的返回类型（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-result_of.html"><span class="kw640">std::<span class="me2">result_of_t</span></span></a><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>F<span class="sy1">></span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">)</span><span class="sy1">></span></span></span> ）。若 <code>U</code> 为对于某类型 <code>T2</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span>T2<span class="sy1">></span></span></span> ，则 <code>then</code> 的返回类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span>T2<span class="sy1">></span></span></span> ，否则它为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span>U<span class="sy1">></span></span></span> 。这被称为<i>隐式解包装</i>。</p>
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<p>若发生隐式解包装且持续返回非法的 <code>future</code> ，则用以 <span class="t-lc"><a href="cpp-thread-future_errc.html">std::future_errc::broken_promise</a></span> 为错误条件的 <span class="t-lc"><a href="cpp-thread-future_error.html">std::future_error</a></span> 类型异常令共享状态就绪。</p>
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<p>此函数返回后， <span class="t-c"><span class="mw-geshi cpp source-cpp">valid<span class="br0">(</span><span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>func</td>
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<td>-</td>
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<td>要附着的持续。</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>与此对象所创建的共享状态关联的 <span class="t-lc">std::experimental::future</span> 对象。对于返回的对象 <span class="t-c"><span class="mw-geshi cpp source-cpp">valid<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <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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<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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