311 lines
36 KiB
HTML
311 lines
36 KiB
HTML
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<title>std::invoke, std::invoke_r</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>invoke, <span style="font-size:0.7em; line-height:130%">std::</span>invoke_r</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-functional.html">functional</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-functional.html"><functional></a></code></div>
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<td rowspan="142">(1)</td>
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<tr class="t-dcl t-since-cxx17 t-until-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> F, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br /></span>
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<p>std<span class="sy4">::</span><span class="me2">invoke_result_t</span><span class="sy1"><</span>F, Args...<span class="sy1">></span><br /></p>
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invoke<span class="br0">(</span> F<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></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> F, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">invoke_result_t</span><span class="sy1"><</span>F, Args...<span class="sy1">></span><br /></p>
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invoke<span class="br0">(</span> F<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></div>
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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">template</span><span class="sy1"><</span> <span class="kw1">class</span> R, <span class="kw1">class</span> F, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> R invoke_r<span class="br0">(</span>F<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></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-cxx23">(C++23 起)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> 以参数 <code>f</code> 调用<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> 对象。如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1116">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> 。此重载仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">is_invocable_v</span><span class="sy1"><</span>F, Args...<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 才参与重载决议。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了若 <code>R</code> 不是可为 cv 限定的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 则将结果隐式转换到 <code>R</code> ，否则舍弃结果。此重载仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">is_invocable_r_v</span><span class="sy1"><</span>R, F, Args...<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 才参与重载决议。</div>
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<p>操作 <i>INVOKE(f, t1, t2, ..., tN)</i> 定义如下：</p>
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<ul>
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<li>若 <code>f</code> 是类 <code>T</code> 的<a href="cpp-language-pointer.html#.E6.8C.87.E5.90.91.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0.E7.9A.84.E6.8C.87.E9.92.88">指向成员函数的指针</a>：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_base_of.html"><span class="kw590">std::<span class="me2">is_base_of</span></span></a><span class="sy1"><</span>T, <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>t1<span class="br0">)</span><span class="sy1">>></span><span class="sy4">::</span><span class="me2">value</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1, t2, ..., tN<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>t1.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span>t2, ..., tN<span class="br0">)</span></span></span></li>
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<li>若 <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>decltype<span class="br0">(</span>t1<span class="br0">)</span><span class="sy1">></span></span></span> 是 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 的特化，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1, t2, ..., tN<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>t1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span>t2, ..., tN<span class="br0">)</span></span></span></li>
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<li>若 <code>t1</code> 不满足前述项目，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1, t2, ..., tN<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="br0">(</span><span class="sy2">*</span>t1<span class="br0">)</span>.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span>t2, ..., tN<span class="br0">)</span></span></span>.</li>
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</ul>
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</dd>
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</dl>
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<ul>
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<li>否则，若 N == 1 且 <code>f</code> 是类 <code>T</code> 的<a href="cpp-language-pointer.html#.E6.8C.87.E5.90.91.E6.95.B0.E6.8D.AE.E6.88.90.E5.91.98.E7.9A.84.E6.8C.87.E9.92.88">指向数据成员的指针</a>：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_base_of.html"><span class="kw590">std::<span class="me2">is_base_of</span></span></a><span class="sy1"><</span>T, <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>t1<span class="br0">)</span><span class="sy1">>></span><span class="sy4">::</span><span class="me2">value</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">t1.<span class="sy2">*</span>f</span></span></li>
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<li>若 <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>decltype<span class="br0">(</span>t1<span class="br0">)</span><span class="sy1">></span></span></span> 是 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 的特化，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">t1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>.<span class="sy2">*</span>f</span></span></li>
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<li>若 <code>t1</code> 不满足前述项目，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="sy2">*</span>t1<span class="br0">)</span>.<span class="sy2">*</span>f</span></span></li>
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</ul>
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</dd>
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</dl>
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<ul>
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<li>否则， <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="br0">(</span>f, t1, t2, ..., tN<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">f<span class="br0">(</span>t1, t2, ..., tN<span class="br0">)</span></span></span> （即 <code>f</code> 是一个<a href="cpp-named_req-FunctionObject.html"><span style="font-style:italic">函数对象</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FunctionObject)</span></a> ）</li>
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</ul>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>f</td>
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<td>-</td>
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<td>要调用的<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> 对象</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>传递给 <code>f</code> 的参数</td>
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</tr>
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</table>
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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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<div class="t-li1"><span class="t-li">1)</span> <code>f</code> 返回的值。</div>
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<div class="t-li1"><span class="t-li">2)</span> <code>f</code> 返回的值隐式转换成 <code>R</code> ，若 <code>R</code> 不是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 。否则为无。</div>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">1)</span>
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<div class="t-noexcept-full"><a href="cpp-language-noexcept_spec.html"><tt>noexcept</tt></a> 说明：
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<div class="t-noexcept-box"><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">is_nothrow_invocable_v</span><span class="sy1"><</span>F, Args...<span class="sy1">></span><span class="br0">)</span></span></span></div>
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</div>
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</div>
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<div class="t-li1"><span class="t-li">2)</span>
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<div class="t-noexcept-full"><a href="cpp-language-noexcept_spec.html"><tt>noexcept</tt></a> 说明：
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<div class="t-noexcept-box"><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">is_nothrow_invocable_r_v</span><span class="sy1"><</span>R, F, Args...<span class="sy1">></span><span class="br0">)</span></span></span></div>
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</div>
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</div>
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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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<table class="eq-fun-cpp-table">
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<tr>
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<th>版本一</th>
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</tr>
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<tr>
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<td>
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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">namespace</span> detail <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> is_reference_wrapper_v <span class="sy1">=</span> <span class="kw2">false</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> U<span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> is_reference_wrapper_v<span class="sy1"><</span><a href="cpp-utility-functional-reference_wrapper.html"><span class="kw1067">std::<span class="me2">reference_wrapper</span></span></a><span class="sy1"><</span>U<span class="sy1">>></span> <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> C, <span class="kw1">class</span> Pointed, <span class="kw1">class</span> T1, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> decltype<span class="br0">(</span><span class="kw4">auto</span><span class="br0">)</span> invoke_memptr<span class="br0">(</span>Pointed C<span class="sy4">::</span><span class="sy2">*</span> f, T1<span class="sy3">&&</span> t1, Args<span class="sy3">&&</span>... <span class="me1">args</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><a href="cpp-types-is_function.html"><span class="kw479">std::<span class="me2">is_function_v</span></span></a><span class="sy1"><</span>Pointed<span class="sy1">></span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><a href="cpp-types-is_base_of.html"><span class="kw591">std::<span class="me2">is_base_of_v</span></span></a><span class="sy1"><</span>C, <a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>T1<span class="sy1">>></span><span class="br0">)</span>
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<span class="kw1">return</span> <span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T1<span class="sy1">></span><span class="br0">(</span>t1<span class="br0">)</span>.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span>is_reference_wrapper_v<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>T1<span class="sy1">>></span><span class="br0">)</span>
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<span class="kw1">return</span> <span class="br0">(</span>t1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
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<span class="kw1">else</span>
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<span class="kw1">return</span> <span class="br0">(</span><span class="br0">(</span><span class="sy2">*</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T1<span class="sy1">></span><span class="br0">(</span>t1<span class="br0">)</span><span class="br0">)</span>.<span class="sy2">*</span>f<span class="br0">)</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
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|
<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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|
static_assert<span class="br0">(</span><a href="cpp-types-is_object.html"><span class="kw487">std::<span class="me2">is_object_v</span></span></a><span class="sy1"><</span>Pointed<span class="sy1">></span> <span class="sy3">&&</span> sizeof...<span class="br0">(</span>args<span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><a href="cpp-types-is_base_of.html"><span class="kw591">std::<span class="me2">is_base_of_v</span></span></a><span class="sy1"><</span>C, <a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>T1<span class="sy1">>></span><span class="br0">)</span>
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<span class="kw1">return</span> <a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T1<span class="sy1">></span><span class="br0">(</span>t1<span class="br0">)</span>.<span class="sy2">*</span>f<span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span>is_reference_wrapper_v<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>T1<span class="sy1">>></span><span class="br0">)</span>
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<span class="kw1">return</span> t1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>.<span class="sy2">*</span>f<span class="sy4">;</span>
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|
<span class="kw1">else</span>
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|
<span class="kw1">return</span> <span class="br0">(</span><span class="sy2">*</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T1<span class="sy1">></span><span class="br0">(</span>t1<span class="br0">)</span><span class="br0">)</span>.<span class="sy2">*</span>f<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="br0">}</span> <span class="co1">// namespace detail</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> F, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">invoke_result_t</span><span class="sy1"><</span>F, Args...<span class="sy1">></span> invoke<span class="br0">(</span>F<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span><span class="br0">)</span>
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<span class="kw1">noexcept</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">is_nothrow_invocable_v</span><span class="sy1"><</span>F, Args...<span class="sy1">></span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><a href="cpp-types-is_member_pointer.html"><span class="kw493">std::<span class="me2">is_member_pointer_v</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>
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<span class="kw1">return</span> detail<span class="sy4">::</span><span class="me2">invoke_memptr</span><span class="br0">(</span>f, <a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
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<span class="kw1">else</span>
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<span class="kw1">return</span> <a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
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|
<span class="br0">}</span></pre></div>
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</div>
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</td>
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</tr>
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<tr>
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<th>版本二</th>
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</tr>
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<tr>
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<td>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<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> R, <span class="kw1">class</span> F, <span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">></span>
|
|
requires std<span class="sy4">::</span><span class="me2">is_invocable_r_v</span><span class="sy1"><</span>R, F, Args...<span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> R invoke_r<span class="br0">(</span>F<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span><span class="br0">)</span>
|
|
<span class="kw1">noexcept</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">is_nothrow_invocable_r_v</span><span class="sy1"><</span>R, F, Args...<span class="sy1">></span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><a href="cpp-types-is_void.html"><span class="kw451">std::<span class="me2">is_void_v</span></span></a><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">)</span>
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|
std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
|
|
<span class="kw1">else</span>
|
|
<span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1116">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 class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
</td>
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|
</tr>
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|
</table>
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<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 <functional></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <type_traits></span>
|
|
|
|
<span class="kw1">struct</span> Foo <span class="br0">{</span>
|
|
Foo<span class="br0">(</span><span class="kw4">int</span> num<span class="br0">)</span> <span class="sy4">:</span> num_<span class="br0">(</span>num<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
|
<span class="kw4">void</span> print_add<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> num_<span class="sy2">+</span>i <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> num_<span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">void</span> print_num<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw1">struct</span> PrintNum <span class="br0">{</span>
|
|
<span class="kw4">void</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span> <span class="kw4">const</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="co1">// 调用自由函数</span>
|
|
std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>print_num, <span class="sy2">-</span><span class="nu0">9</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 调用 lambda</span>
|
|
std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span><span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> print_num<span class="br0">(</span><span class="nu0">42</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 调用成员函数</span>
|
|
<span class="kw4">const</span> Foo foo<span class="br0">(</span><span class="nu0">314159</span><span class="br0">)</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span><span class="sy3">&</span>Foo<span class="sy4">::</span><span class="me2">print_add</span>, foo, <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 调用（访问）数据成员</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"num_: "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span><span class="sy3">&</span>Foo<span class="sy4">::</span><span class="me2">num_</span>, foo<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 调用函数对象</span>
|
|
std<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>PrintNum<span class="br0">(</span><span class="br0">)</span>, <span class="nu0">18</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co2"># if defined(__cpp_lib_invoke_r)</span>
|
|
<span class="kw4">auto</span> add <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> x, <span class="kw4">int</span> y<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> x <span class="sy2">+</span> y<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw4">auto</span> ret <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">invoke_r</span><span class="sy1"><</span><span class="kw4">float</span><span class="sy1">></span><span class="br0">(</span>add, <span class="nu0">11</span>, <span class="nu0">22</span><span class="br0">)</span><span class="sy4">;</span>
|
|
static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>ret<span class="br0">)</span>, <span class="kw4">float</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> ret <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">invoke_r</span><span class="sy1"><</span><span class="kw4">void</span><span class="sy1">></span><span class="br0">(</span>print_num, <span class="nu0">44</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="co2"># endif</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>可能的输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">-9
|
|
42
|
|
314160
|
|
num_: 314159
|
|
18
|
|
33
|
|
44</pre></div>
|
|
</div>
|
|
</div>
|
|
<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-utility-functional-mem_fn.html"><span class="t-lines"><span>mem_fn</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>从成员指针创建出函数对象<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-types-result_of.html"><span class="t-lines"><span>result_of</span><span>invoke_result</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>推导以一组实参调用一个可调用对象的结果类型<br />
|
|
<span class="t-mark">(类模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-types-is_invocable.html"><span class="t-lines"><span>is_invocable</span><span>is_invocable_r</span><span>is_nothrow_invocable</span><span>is_nothrow_invocable_r</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>检查类型能否以给定的实参类型调用（如同以 <span class="t-lc"><strong class="selflink">std::invoke</strong></span>）<br />
|
|
<span class="t-mark">(类模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-apply.html"><span class="t-lines"><span>apply</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>以一个实参的元组来调用函数<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|