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<div class="identifier-type">function template</div><div class="header"><functional></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">invoke</span><span class="cpp cpp17" title="C++17で追加">(C++17)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">F</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="p">...</span><span class="w"> </span><span class="n">Args</span><span class="o">></span>
<span class="w"> </span><span class="n"><a href="../type_traits/invoke_result.html">invoke_result_t</a></span><span class="o"><</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p">...</span><span class="o">></span><span class="w"> </span><span class="n">invoke</span><span class="p">(</span><span class="n">F</span><span class="o">&&</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="o">&&</span><span class="p">...</span><span class="w"> </span><span class="n">args</span><span class="p">)</span>
<span class="w"> </span><span class="k">noexcept</span><span class="p">(</span><span class="n"><a href="../type_traits/is_nothrow_invocable.html">is_nothrow_invocable_v</a></span><span class="o"><</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p">...</span><span class="o">></span><span class="p">);</span><span class="w"> </span><span class="c1">//C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">F</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="p">...</span><span class="w"> </span><span class="n">Args</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><a href="../type_traits/invoke_result.html">invoke_result_t</a></span><span class="o"><</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p">...</span><span class="o">></span><span class="w"> </span><span class="n">invoke</span><span class="p">(</span><span class="n">F</span><span class="o">&&</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="o">&&</span><span class="p">...</span><span class="w"> </span><span class="n">args</span><span class="p">)</span>
<span class="w"> </span><span class="k">noexcept</span><span class="p">(</span><span class="n"><a href="../type_traits/is_nothrow_invocable.html">is_nothrow_invocable_v</a></span><span class="o"><</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p">...</span><span class="o">></span><span class="p">);</span><span class="w"> </span><span class="c1">//C++20</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>関数呼び出し可能なオブジェクト<code>f</code>とその引数<code>args...</code>の組み合わせで<a href="../concepts/Invoke.html"><em>INVOKE</em></a>要件に従った関数呼び出しを行う。</p>
<p><a href="../concepts/Invoke.html"><em>INVOKE</em></a>要件とはC++における関数呼び出しという性質を抽象化しまとめた概念であり、<code>invoke</code>はその実体化、すなわち関数呼び出しという操作を統一したものである。</p>
<h2>要件</h2>
<p>型<code>F</code>および<code>Args...</code>の組み合わせで<a href="../concepts/Invoke.html"><em>INVOKE</em></a>要件に従った関数呼び出しが可能であり、<a class="cpprefjp-defined-word" data-desc="関数呼び出し時に、同名の関数の中から実際に呼び出す関数を決定する処理。このときの候補になることを、オーバーロード解決に参加するという">オーバーロード解決</a>の結果が曖昧にならないこと。そうでない場合はコンパイルエラーとなる。</p>
<h2>引数</h2>
<ul>
<li><code>f</code> -- <a href="../concepts/Callable.html"><em>Callable</em></a> オブジェクト（関数ポインタ/参照・関数オブジェクト・メンバポインタ）</li>
<li><code>args...</code> -- <code>f</code>に与える引数列。<code>f</code>がメンバポインタである場合は対応するクラスのオブジェクト（もしくはその<a href="reference_wrapper.html">reference_wrapper</a>）が<code>args...</code>の先頭になければならない</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<p><code>f</code>と<code>args...</code>により<a href="../concepts/Invoke.html"><em>INVOKE</em></a>要件に従った関数呼び出しを行い、その結果を<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>として返す。</p>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<p><code>f</code>の<code>args...</code>による関数呼び出しに際して<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を投げない（<code><a href="../type_traits/is_nothrow_invocable.html">is_nothrow_invocable_v<F, Args...></a> == true</code>）ならば、この関数も<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を投げない。</p>
<h2>例</h2>
<p><div class="yata" id="12790455cdc91d873c2b90818805f1fbb0245c6f"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../functional.html"><functional></a></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">functor</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="k">operator</span><span class="p">()()</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="k">operator</span><span class="p">()(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">n</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">has_member</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">member_function</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">n</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">member_object</span><span class="p">;</span>
<span class="p">};</span>
<span class="k">auto</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mf">3.14159265359</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">auto</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mf">2.71828182846</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">auto</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="kt">int</span><span class="p">,</span><span class="kt">int</span><span class="p">)</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mf">3.14159265359</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">int</span><span class="w"> </span><span class="n">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">functor</span><span class="w"> </span><span class="n">fobj</span><span class="p">{};</span>
<span class="w"> </span><span class="c1">//関数オブジェクト呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="n">fobj</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="n">fobj</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">has_member</span><span class="w"> </span><span class="n">obj</span><span class="p">{</span><span class="mi">25</span><span class="p">};</span>
<span class="w"> </span><span class="c1">//メンバ関数呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="o">&</span><span class="n">has_member</span><span class="o">::</span><span class="n">member_function</span><span class="p">,</span><span class="w"> </span><span class="n">obj</span><span class="p">,</span><span class="w"> </span><span class="mi">50</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">//メンバ変数呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="o">&</span><span class="n">has_member</span><span class="o">::</span><span class="n">member_object</span><span class="p">,</span><span class="w"> </span><span class="n">obj</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">ref</span><span class="p">(</span><span class="n">obj</span><span class="p">);</span>
<span class="w"> </span><span class="c1">//reference_wrapperからのメンバ関数呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="o">&</span><span class="n">has_member</span><span class="o">::</span><span class="n">member_function</span><span class="p">,</span><span class="w"> </span><span class="n">ref</span><span class="p">,</span><span class="w"> </span><span class="mi">50</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">//reference_wrapperからのメンバ変数呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="o">&</span><span class="n">has_member</span><span class="o">::</span><span class="n">member_object</span><span class="p">,</span><span class="w"> </span><span class="n">ref</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">//関数呼び出し</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">//フリー関数は一度関数ポインタにしないとオーバーロード解決できない</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">((</span><span class="kt">double</span><span class="p">(</span><span class="o">*</span><span class="p">)(</span><span class="kt">int</span><span class="p">))</span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::invoke</span></span><span class="p">((</span><span class="kt">double</span><span class="p">(</span><span class="o">*</span><span class="p">)(</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="p">))</span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">//コンパイルエラー</span>
<span class="w"> </span><span class="c1">//<a href="../iostream/cout.html">std::cout</a> << <span style="color:#ff0000">std::invoke</span>(g, 10) << <a href="../ostream/endl.html">std::endl</a>;</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>10
100
50
25
50
25
3.14159
2.71828
3.14159
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++17</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../implementation.html#gcc">GCC</a>: ??</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2015 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2017 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="invoke_r.html">invoke_r</a></code></li>
<li><code><a href="../type_traits/invoke_result.html">invoke_result</a></code></li>
<li><code><a href="../type_traits/is_invocable.html">is_invocable</a></code></li>
<li><code><a href="../type_traits/is_nothrow_invocable.html">is_nothrow_invocable</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://faithandbrave.hateblo.jp/entry/2016/09/07/173344" target="_blank">C++1z INVOKEコンセプトに従った関数呼び出しをするinvoke()関数 - Faith and Brave - C++で遊ぼう</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4169.html" target="_blank">N4169 A proposal to add invoke function template (Revision 1)</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1065r2.html" target="_blank">P1065R2 constexpr INVOKE</a></li>
</ul></div>
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