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<div class="identifier-type">class template</div><div class="header"><coroutine></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">coroutine_handle</span><span class="cpp cpp20" title="C++20で追加">(C++20)</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="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Promise</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">coroutine_handle</span><span class="p">;</span>
<span class="w"> </span><span class="k">template</span><span class="o"><></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">coroutine_handle</span><span class="o"><</span><span class="kt">void</span><span class="o">></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// (メンバ宣言は省略)</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Promise</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">coroutine_handle</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// (メンバ宣言は省略)</span>
<span class="w"> </span><span class="p">};</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>コルーチンに対応するコルーチンハンドル。
テンプレートパラメータ<code>Promise</code>には、コルーチンのPromise型を指定する。</p>
<p>コルーチンハンドルはアプリケーションコードからの直接アクセスを想定した機能ではなく、コルーチンライブラリ提供クラス内部に隠蔽される構造が一般的である。
例: 後述サンプルコードでは<code>task</code>クラス内に隠蔽されており、コルーチン<code>f</code>や関数<code>main</code>から間接的に利用される。</p>
<p><code>coroutine_handle<void></code>または単に<code>coroutine_handle<></code>は、Promise型について型消去(Type-erased)されたコルーチンハンドルとして取り扱える。
コルーチンのPromise型を明示した<code>coroutine_handle<Promise></code>から<code>coroutine_handle<></code>へと暗黙変換が可能となっている。</p>
<p>C++コルーチンとC API（コールバック関数へのポインタと<code>void*</code>をとる関数）との組合せ利用を可能とするため、<code>coroutine_handle</code>とポインタ型<code>void*</code>との相互変換がサポートされる。</p>
<p>ユーザプログラムが<code>coroutine_handle</code>の明示特殊化または部分特殊化を宣言した場合、その<a class="cpprefjp-defined-word" data-desc="未定義の動作。処理系は予期せぬ動作をする可能性がある。要するに動作保証対象外。undefined behavior (UB)。" href="../../implementation-compliance.html#dfn-undefined-behavior">動作は未定義</a>とされる。</p>
<h2>メンバ関数</h2>
<h3>構築・リセット</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/op_constructor.html">(constructor)</a></code></td>
<td>コンストラクタ</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="coroutine_handle/op_assign.html">operator=</a></code></td>
<td>代入演算子</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>エクスポート</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/address.html">address</a></code></td>
<td>コルーチンハンドルに対応するアドレス値</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>変換</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>operator coroutine_handle<></code></td>
<td>型消去されたコルーチンハンドルを返す</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>観測</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/op_bool.html">operator bool</a></code></td>
<td>有効なコルーチンか確認</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="coroutine_handle/done.html">done</a></code></td>
<td>最終サスペンドポイントで中断状態にあるか確認</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>再開</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/resume.html">operator()</a></code></td>
<td>中断状態にあるコルーチンを再開</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="coroutine_handle/resume.html">resume</a></code></td>
<td>中断状態にあるコルーチンを再開</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="coroutine_handle/destroy.html">destroy</a></code></td>
<td>中断状態にあるコルーチンを破棄</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>Promiseアクセス</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/promise.html">promise</a></code></td>
<td>Promiseオブジェクトの参照（<code>coroutine_handle<Promise></code>のみ）</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h2>静的メンバ関数</h2>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="coroutine_handle/from_promise.html">from_promise</a></code></td>
<td>Promiseオブジェクトから対応するコルーチンハンドルへ変換（<code>coroutine_handle<Promise></code>のみ）</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="coroutine_handle/from_address.html">from_address</a></code></td>
<td>アドレス値から対応するコルーチンハンドルへ変換</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h2>非メンバ関数</h2>
<h3>ハッシュサポート</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>template<class T> struct hash</code></td>
<td>先行宣言(class template)</td>
<td>C++20</td>
</tr>
<tr>
<td><code>template<class P> struct hash<coroutine_handle<P>></code></td>
<td><code>hash</code>の<code>coroutine_handle<P></code>に対する特殊化</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>比較演算子</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>bool operator==(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>等値比較</td>
<td>C++20</td>
</tr>
<tr>
<td><code>bool operator!=(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>非等値比較 (<code>==</code>により使用可能)</td>
<td>C++20</td>
</tr>
<tr>
<td><code>strong_ordering operator<=>(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>三方比較</td>
<td>C++20</td>
</tr>
<tr>
<td><code>bool operator<(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>左辺が右辺より小さいかを判定する (<code><=></code>により使用可能)</td>
<td>C++20</td>
</tr>
<tr>
<td><code>bool operator<=(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>左辺が右辺以下を判定する (<code><=></code>により使用可能)</td>
<td>C++20</td>
</tr>
<tr>
<td><code>bool operator>(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>左辺が右辺より大きいかを判定する (<code><=></code>により使用可能)</td>
<td>C++20</td>
</tr>
<tr>
<td><code>bool operator>=(coroutine_handle<>, coroutine_handle<>);</code></td>
<td>左辺が右辺以上かを判定する (<code><=></code>により使用可能)</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<p><code>coroutine_handle</code>同士の比較は、<code><a href="coroutine_handle/address.html">address</a></code>が返すアドレス値を用いて比較演算が行われる。</p>
<h2>例</h2>
<p><div class="yata" id="e3b5440097f76cc0881e47bbbd8f773fac52a196"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../coroutine.html"><coroutine></a></span>
<span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../utility.html"><utility></a></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">task</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">promise_type</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">value_</span><span class="p">;</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">get_return_object</span><span class="p">()</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">task</span><span class="p">{</span><span class="o">*</span><span class="k">this</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="n">initial_suspend</span><span class="p">()</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"><a href="suspend_never.html">std::suspend_never</a></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="n">final_suspend</span><span class="p">()</span><span class="w"> </span><span class="k">noexcept</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"><a href="suspend_always.html">std::suspend_always</a></span><span class="p">{};</span><span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">return_value</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">value_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">x</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">unhandled_exception</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">terminate</span><span class="p">();</span><span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="o">~</span><span class="n">task</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">coro_</span><span class="p">)</span>
<span class="w"> </span><span class="n">coro_</span><span class="p">.</span><span class="n">destroy</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n">task</span><span class="p">(</span><span class="n">task</span><span class="w"> </span><span class="k">const</span><span class="o">&</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">delete</span><span class="p">;</span>
<span class="w"> </span><span class="n">task</span><span class="p">(</span><span class="n">task</span><span class="o">&&</span><span class="w"> </span><span class="n">rhs</span><span class="p">)</span>
<span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">coro_</span><span class="p">(</span><span class="n"><a href="../utility/exchange.html">std::exchange</a></span><span class="p">(</span><span class="n">rhs</span><span class="p">.</span><span class="n">coro_</span><span class="p">,</span><span class="w"> </span><span class="k">nullptr</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">get</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">coro_</span><span class="p">.</span><span class="n"><a href="coroutine_handle/done.html">done()</a></span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">coro_</span><span class="p">.</span><span class="n"><a href="coroutine_handle/resume.html">resume()</a></span><span class="p">;</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">coro_</span><span class="p">.</span><span class="n"><a href="coroutine_handle/promise.html">promise()</a></span><span class="p">.</span><span class="n">value_</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="k">private</span><span class="o">:</span>
<span class="w"> </span><span class="k">explicit</span><span class="w"> </span><span class="n">task</span><span class="p">(</span><span class="n">promise_type</span><span class="o">&</span><span class="w"> </span><span class="n">p</span><span class="p">)</span>
<span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">coro_</span><span class="p">(</span><span class="n"><span style="color:#ff0000">std::coroutine_handle<promise_type></span></span><span class="o">::</span><span class="n"><a href="coroutine_handle/from_promise.html">from_promise</a></span><span class="p">(</span><span class="n">p</span><span class="p">))</span><span class="w"> </span><span class="p">{}</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::coroutine_handle<promise_type></span></span><span class="w"> </span><span class="n">coro_</span><span class="p">;</span>
<span class="p">};</span>
<span class="n">task</span><span class="w"> </span><span class="nf">f</span><span class="p">()</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="s">"coroutine"</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">co_return</span><span class="w"> </span><span class="mi">42</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">c</span><span class="w"> </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"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"main"</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="kt">int</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">get</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="s">"result="</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">r</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="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>coroutine
main
result=42
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++20</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>: 11.1 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>関連項目</h2>
<ul>
<li><a href="../../lang/cpp20/coroutines.html">C++20 コルーチン</a></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://cplusplus.github.io/LWG/issue3460" target="_blank">LWG3460 Unimplementable <code>noop_coroutine_handle</code> guarantees</a></li>
</ul></div>
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