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<header data-kunai-mdinfo="{"meta": {"header": ["functional"], "namespace": ["std"], "class": ["function"], "id-type": ["function"], "cpp": ["cpp11"]}, "sources": [{"id": "4659cefb7ebd19af9d11adc6d13187813988667b", "source": "#include <cassert>\n#include <iostream>\n#include <functional>\n\nstruct ident_functor {\n int operator()(int x) const\n { return x; }\n};\n\nint ident_func(int x)\n{ return x; }\n\nstruct X {\n int value;\n X() : value(3) {}\n\n int ident_member_func(int x) const\n { return x; }\n};\n\nint main()\n{\n // (1)\n // \u30c7\u30d5\u30a9\u30eb\u30c8\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\n // \u7a7a\u306efunction\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u4f5c\u308b\n {\n std::function<int(int)> f;\n assert(!f);\n }\n\n // (2)\n // \u30cc\u30eb\u30dd\u30a4\u30f3\u30bf\u3092\u53d7\u3051\u53d6\u308b\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\n // \u30c7\u30d5\u30a9\u30eb\u30c8\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\u3068\u540c\u69d8\u3001\u7a7a\u306efunction\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u4f5c\u308b\n {\n std::function<int(int)> f = nullptr;\n assert(!f);\n }\n\n // (3)\n // \u30b3\u30d4\u30fc\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_functor();\n std::function<int(int)> g = f;\n\n int result = g(1);\n std::cout << \"(3) : \" << result << std::endl;\n }\n\n // (4)\n // \u30e0\u30fc\u30d6\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_functor();\n std::function<int(int)> g = std::move(f);\n\n int result = g(1);\n std::cout << \"(4) : \" << result << std::endl;\n }\n\n // (5)\n // \u95a2\u6570\u30dd\u30a4\u30f3\u30bf\u3092\u53d7\u3051\u53d6\u3063\u3066\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_func;\n\n int result = f(1);\n std::cout << \"(5) function pointer : \" << result << std::endl;\n }\n\n // (5)\n // \u95a2\u6570\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u53d7\u3051\u53d6\u3063\u3066\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_functor();\n\n int result = f(1);\n std::cout << \"(5) function object : \" << result << std::endl;\n }\n\n // (5)\n // \u30e1\u30f3\u30d0\u95a2\u6570\u30dd\u30a4\u30f3\u30bf\u3092\u53d7\u3051\u53d6\u3063\u305f\u69cb\u7bc9\n {\n std::function<int(const X&, int)> f = &X::ident_member_func;\n\n X x;\n int result = f(x, 1);\n std::cout << \"(5) member function pointer : \" << result << std::endl;\n }\n\n // (5)\n // \u30e1\u30f3\u30d0\u5909\u6570\u30dd\u30a4\u30f3\u30bf\u3092\u53d7\u3051\u53d6\u3063\u305f\u69cb\u7bc9\n {\n std::function<int(const X&)> f = &X::value;\n\n X x;\n int result = f(x);\n std::cout << \"(5) member variable pointer : \" << result << std::endl;\n }\n\n // (6)\n // \u30a2\u30ed\u30b1\u30fc\u30bf\u3092\u53d7\u3051\u53d6\u3063\u3066\u7a7a\u306efunction\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u69cb\u7bc9\n {\n // \u203b\u3053\u3053\u3067\u306fint\u578b\u3092\u5bfe\u8c61\u3068\u3059\u308b\u30a2\u30ed\u30b1\u30fc\u30bf\u3092\u6e21\u3057\u3066\u3044\u308b\u304c\u3001\u5185\u90e8\u3067\u9069\u5207\u306a\u95a2\u6570\u306e\u578b\u306brebind\u3057\u3066\u4f7f\u308f\u308c\u308b\u3002\n std::function<int(int)> f(std::allocator_arg, std::allocator<int>());\n assert(!f);\n }\n\n // (7)\n // \u30a2\u30ed\u30b1\u30fc\u30bf\u3068\u30cc\u30eb\u30dd\u30a4\u30f3\u30bf\u3092\u53d7\u3051\u53d6\u3063\u3066\u3001\u7a7a\u306efunction\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u69cb\u7bc9\n {\n std::function<int(int)> f(std::allocator_arg, std::allocator<int>(), nullptr);\n assert(!f);\n }\n\n // (8)\n // \u30a2\u30ed\u30b1\u30fc\u30bf\u3092\u53d7\u3051\u53d6\u308a\u3001function\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u30b3\u30d4\u30fc\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_functor();\n std::function<int(int)> g(std::allocator_arg, std::allocator<int>(), f);\n\n int result = g(1);\n std::cout << \"(8) : \" << result << std::endl;\n }\n\n // (9)\n // \u30a2\u30ed\u30b1\u30fc\u30bf\u3092\u53d7\u3051\u53d6\u308a\u3001function\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u30e0\u30fc\u30d6\u69cb\u7bc9\n {\n std::function<int(int)> f = ident_functor();\n std::function<int(int)> g(std::allocator_arg, std::allocator<int>(), std::move(f));\n\n int result = g(1);\n std::cout << \"(9) : \" << result << std::endl;\n }\n\n // (10)\n // \u95a2\u6570\u30dd\u30a4\u30f3\u30bf\u3001\u95a2\u6570\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3001\u30e1\u30f3\u30d0\u30dd\u30a4\u30f3\u30bf\u306e\u3044\u305a\u308c\u304b\u3092\u53d7\u3051\u53d6\u3063\u305f\u69cb\u7bc9\n {\n std::function<int(int)> f(std::allocator_arg, std::allocator<int>(), ident_functor());\n\n int result = f(1);\n std::cout << \"(10) : \" << result << std::endl;\n }\n}\n"}], "page_id": ["reference", "functional", "function", "op_constructor"]}">
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最終更新日時(UTC):
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2025年07月08日 15時33分39秒
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<div class="identifier-type">function</div><div class="header"><functional></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="class" title="class function">function::</span><span class="token">コンストラクタ</span><span class="cpp cpp11" title="C++11で追加">(C++11)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="n">function</span><span class="p">()</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (1) C++11</span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../cstddef/nullptr_t.html">nullptr_t</a></span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (2) C++11</span>
<span class="n">function</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">function</span><span class="o">&</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (3) C++11</span>
<span class="n">function</span><span class="p">(</span><span class="n">function</span><span class="o">&&</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (4) C++11</span>
<span class="n">function</span><span class="p">(</span><span class="n">function</span><span class="o">&&</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (4) C++20</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="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n">F</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (5) C++11</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="o">></span>
<span class="n">function</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="c1">// (5) C++23</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">Alloc</span><span class="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">allocator_arg_t</a></span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Alloc</span><span class="o">&</span><span class="w"> </span><span class="n">alloc</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (6) C++17で削除</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">Alloc</span><span class="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">allocator_arg_t</a></span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Alloc</span><span class="o">&</span><span class="w"> </span><span class="n">alloc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../cstddef/nullptr_t.html">nullptr_t</a></span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (7) C++17で削除</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">Alloc</span><span class="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">allocator_arg_t</a></span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Alloc</span><span class="o">&</span><span class="w"> </span><span class="n">alloc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">function</span><span class="o">&</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (8) C++17で削除</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">Alloc</span><span class="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">allocator_arg_t</a></span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Alloc</span><span class="o">&</span><span class="w"> </span><span class="n">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">function</span><span class="o">&&</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (9) C++17で削除</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="w"> </span><span class="nc">Alloc</span><span class="o">></span>
<span class="n">function</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">allocator_arg_t</a></span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Alloc</span><span class="o">&</span><span class="w"> </span><span class="n">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (10) C++17で削除</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>function</code>オブジェクトを構築する。</p>
<ul>
<li>(1) : <a class="cpprefjp-defined-word" data-desc="デフォルト初期化。`T x;`構文での初期化。トリビアルにデフォルト構築可能な型の場合は初期化されず（オブジェクトのlifetimeは開始される）、そうではないクラス型はデフォルトコンストラクタで初期化する。配列型の場合は各要素が再帰的にデフォルト初期化される">デフォルト構築</a>。空の<code>function</code>オブジェクトを構築する</li>
<li>(2) : <code>nullptr</code>からの構築。空の<code>function</code>オブジェクトを構築する</li>
<li>(3) : コピー構築する</li>
<li>(4) : ムーブ構築する</li>
<li>(5) : 任意の型の関数ポインタ、メンバポインタ、関数オブジェクトを受け取って構築する</li>
<li>(6) : アロケータをとって空の<code>function</code>オブジェクトを構築する</li>
<li>(7) : アロケータと<code>nullptr</code>をとって空の<code>function</code>オブジェクトを構築する</li>
<li>(8) : アロケータをとってコピー構築する</li>
<li>(9) : アロケータをとってムーブ構築する</li>
<li>(10) : アロケータと、任意の型の関数ポインタ、メンバポインタ、関数オブジェクトを受け取って構築する</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Constraints。関数であればオーバーロード解決に参加するための条件、それ以外であれば受け付ける型の条件">テンプレートパラメータ制約</a></h2>
<p><code><a href="../../type_traits/decay.html">decay_t</a><F></code>を<code>FD</code>として、</p>
<ul>
<li>(5) :<ul>
<li>C++11<ul>
<li><code>F</code>は、パラメータとして<code>ArgTypes...</code>型をとり、<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<code>R</code>型を返す関数ポインタ、メンバ関数ポインタ、メンバ変数ポインタ、または関数オブジェクトであること</li>
</ul>
</li>
<li>C++23<ul>
<li><code>F</code>が<code>function</code>ではないこと</li>
<li><code>FD</code>は、パラメータとして<code>ArgTypes...</code>型をとり、<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<code>R</code>型を返す関数ポインタ、メンバ関数ポインタ、メンバ変数ポインタ、または関数オブジェクトであること</li>
</ul>
</li>
</ul>
</li>
<li>(10) :<ul>
<li><code>F</code>はコピー構築可能であること</li>
<li><code>F</code>のコピーコンストラクタとデストラクタは、<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>を投げるべきではない</li>
<li><code>F</code>は、パラメータとして<code>ArgTypes...</code>型をとり、<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<code>R</code>型を返す関数ポインタ、メンバ関数ポインタ、メンバ変数ポインタ、または関数オブジェクトであること</li>
</ul>
</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Mandates。満たさなければプログラムが不適格となる要件。この要件は、オーバーロード解決によって選択された関数内での`static_assert`の定数条件式や、関数に対するdelete宣言などで表現できる">適格要件</a></h2>
<ul>
<li>(5) :<ul>
<li>C++11<ul>
<li><code>F</code>はコピー構築可能であること</li>
<li><code>F</code>は、パラメータとして<code>ArgTypes...</code>型をとり、<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<code>R</code>型を返す関数ポインタ、メンバ関数ポインタ、メンバ変数ポインタ、または関数オブジェクトであること。</li>
</ul>
</li>
<li>C++23<ul>
<li><code>FD</code>はコピー構築可能であること</li>
<li><code>FD</code>は<code>F</code>から構築可能であること</li>
</ul>
</li>
</ul>
</li>
</ul>
<h2>効果</h2>
<ul>
<li>(1), (2) : 関数を持たない空の<code>function</code>オブジェクトを構築する。この方法で構築した後、<code><a href="op_bool.html">operator bool</a></code>は<code>false</code>を返す。</li>
<li>(3) : <code>f</code>が保持する関数、または関数オブジェクトをコピーする。</li>
<li>(4) : <code>f</code>が保持する状態を<code>*this</code>に移動する。移動された後の<code>f</code>は、<a class="cpprefjp-defined-word" data-desc="未規定の動作。事前の断りなく処理系によって異なる動作をする" href="../../../implementation-compliance.html#dfn-unspecified-behavior">未規定</a>な値を持つ有効な状態となる。</li>
<li>(5) : <code>f</code>がヌルの関数ポインタ、もしくはメンバポインタである場合、構築後の<code><a href="op_bool.html">operator bool</a></code>は<code>false</code>を返す。<code>f</code>が有効な関数ポインタ、メンバポインタ、もしくは関数オブジェクトである場合は、<code>f</code>が持つターゲットを<code>*this</code>に移動する。</li>
<li>(6), (7) : アロケータを設定し、関数を持たない空の<code>function</code>オブジェクトを構築する。この方法で構築した後、<code><a href="op_bool.html">operator bool</a></code>は<code>false</code>を返す。</li>
<li>(9) : アロケータを設定し、<code>f</code>が保持する状態を<code>*this</code>に移動する。移動された後の<code>f</code>は、<a class="cpprefjp-defined-word" data-desc="未規定の動作。事前の断りなく処理系によって異なる動作をする" href="../../../implementation-compliance.html#dfn-unspecified-behavior">未規定</a>な値を持つ有効な状態となる。</li>
<li>(10) : アロケータを設定する。<code>f</code>がヌルの関数ポインタ、もしくはメンバポインタである場合、構築後の<code><a href="op_bool.html">operator bool</a></code>は<code>false</code>を返す。<code>f</code>が有効な関数ポインタ、メンバポインタ、もしくは関数オブジェクトである場合は、<code>f</code>が持つターゲットを<code>*this</code>に移動する。</li>
</ul>
<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>
<ul>
<li>(3), (8) : <code>f</code>が<code><a href="../reference_wrapper.html">reference_wrapper</a></code>か関数ポインタを保持している場合は、<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>を投げるべきではない。<code>f</code>が関数オブジェクトを保持している場合は、そのコピーコンストラクタが<code><a href="../../new/bad_alloc.html">bad_alloc</a></code>やその他の<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>を投げる可能性がある。</li>
<li>(10) : <code>f</code>が<code><a href="../reference_wrapper.html">reference_wrapper</a></code>か関数ポインタを保持している場合は、<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>を投げるべきではない。<code>f</code>が関数オブジェクトを保持している場合は、そのコピーコンストラクタもしくはムーブコンストラクタが<code><a href="../../new/bad_alloc.html">bad_alloc</a></code>やその他の<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>を投げる可能性がある。</li>
</ul>
<h2>備考</h2>
<ul>
<li>(5), (10) : <ul>
<li>C++14 : <code>F</code>が、パラメータとして<code>ArgTypes...</code>型をとり、<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<code>R</code>型を返す関数ポインタ、メンバ関数ポインタ、メンバ変数ポインタ、または関数オブジェクトでない場合、この関数は<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>から除外される。</li>
</ul>
</li>
</ul>
<h2>削除の詳細</h2>
<ul>
<li>(6)-(10) : このクラスのメモリアロケータサポートは、ほとんどの標準ライブラリ実装で使用されず、メモリアロケータを使用する必要がなかった。そのため、実装もされなかったことでユーザーにも使われてこなかったため、この機能を削除した。</li>
</ul>
<h2>例</h2>
<p><div class="yata" id="4659cefb7ebd19af9d11adc6d13187813988667b"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../cassert.html"><cassert></a></span>
<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">ident_functor</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">operator</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="k">const</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">x</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">ident_func</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="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">x</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">X</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="n">X</span><span class="p">()</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">value</span><span class="p">(</span><span class="mi">3</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">ident_member_func</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="k">const</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">x</span><span class="p">;</span><span class="w"> </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="c1">// (1)</span>
<span class="w"> </span><span class="c1">// デフォルトコンストラクタ</span>
<span class="w"> </span><span class="c1">// 空のfunctionオブジェクトを作る</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</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="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="o">!</span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// (2)</span>
<span class="w"> </span><span class="c1">// ヌルポインタを受け取るコンストラクタ</span>
<span class="w"> </span><span class="c1">// デフォルトコンストラクタと同様、空のfunctionオブジェクトを作る</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">nullptr</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="o">!</span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// (3)</span>
<span class="w"> </span><span class="c1">// コピー構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">();</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">g</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="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="mi">1</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">"(3) : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (4)</span>
<span class="w"> </span><span class="c1">// ムーブ構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">();</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../../utility/move.html">std::move</a></span><span class="p">(</span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="mi">1</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">"(4) : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (5)</span>
<span class="w"> </span><span class="c1">// 関数ポインタを受け取って構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_func</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="mi">1</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">"(5) function pointer : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (5)</span>
<span class="w"> </span><span class="c1">// 関数オブジェクトを受け取って構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">();</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="mi">1</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">"(5) function object : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (5)</span>
<span class="w"> </span><span class="c1">// メンバ関数ポインタを受け取った構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">X</span><span class="o">&</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&</span><span class="n">X</span><span class="o">::</span><span class="n">ident_member_func</span><span class="p">;</span>
<span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="n">x</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="mi">1</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">"(5) member function pointer : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (5)</span>
<span class="w"> </span><span class="c1">// メンバ変数ポインタを受け取った構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">X</span><span class="o">&</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&</span><span class="n">X</span><span class="o">::</span><span class="n">value</span><span class="p">;</span>
<span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="n">x</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="n">x</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">"(5) member variable pointer : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (6)</span>
<span class="w"> </span><span class="c1">// アロケータを受け取って空のfunctionオブジェクトを構築</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// ※ここではint型を対象とするアロケータを渡しているが、内部で適切な関数の型にrebindして使われる。</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">std::allocator_arg</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../memory/allocator.html">std::allocator</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">());</span>
<span class="w"> </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="o">!</span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// (7)</span>
<span class="w"> </span><span class="c1">// アロケータとヌルポインタを受け取って、空のfunctionオブジェクトを構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">std::allocator_arg</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../memory/allocator.html">std::allocator</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(),</span><span class="w"> </span><span class="k">nullptr</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="o">!</span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// (8)</span>
<span class="w"> </span><span class="c1">// アロケータを受け取り、functionオブジェクトをコピー構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">();</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">std::allocator_arg</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../memory/allocator.html">std::allocator</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(),</span><span class="w"> </span><span class="n">f</span><span class="p">);</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="mi">1</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">"(8) : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (9)</span>
<span class="w"> </span><span class="c1">// アロケータを受け取り、functionオブジェクトをムーブ構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">();</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">std::allocator_arg</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../memory/allocator.html">std::allocator</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(),</span><span class="w"> </span><span class="n"><a href="../../utility/move.html">std::move</a></span><span class="p">(</span><span class="n">f</span><span class="p">));</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="mi">1</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">"(9) : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="w"> </span><span class="c1">// (10)</span>
<span class="w"> </span><span class="c1">// 関数ポインタ、関数オブジェクト、メンバポインタのいずれかを受け取った構築</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">function</span><span class="o"><</span><span class="kt">int</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="n"><a href="../../memory/allocator_arg_t.html">std::allocator_arg</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../memory/allocator.html">std::allocator</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(),</span><span class="w"> </span><span class="n">ident_functor</span><span class="p">());</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="mi">1</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">"(10) : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</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="p">}</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>(3) : 1
(4) : 1
(5) function pointer : 1
(5) function object : 1
(5) member function pointer : 1
(5) member variable pointer : 3
(8) : 1
(9) : 1
(10) : 1
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++11</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../../implementation.html#clang">Clang</a>: 3.0 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../../implementation.html#gcc">GCC</a>: 4.3.6(アロケータを受け取るバージョンは、4.8.2時点でサポートされていない) <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>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2308.html" target="_blank">N2308 Adding allocator support to <code>std::function</code> for C++0x</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2132" target="_blank">LWG Issue 2132. <code>std::function</code> ambiguity</a><ul>
<li>C++14から、(5)と(10)でシグニチャが合わない関数オブジェクトが渡された場合に、SFINAEされるようになった。</li>
</ul>
</li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0302r1.html" target="_blank">P0302R1 Removing Allocator Support in <code>std::function</code> (rev 1)</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0771r1.pdf" target="_blank">P0771R1 std::function move constructor should be noexcept</a></li>
<li><a href="https://cplusplus.github.io/LWG/issue2774" target="_blank">LWG Issue 2774. <code>std::function</code> construction vs assignment</a><ul>
<li>C++23から、<code>function(F)</code>の<a class="cpprefjp-defined-word" data-desc="同名の関数を異なる引数・テンプレート・制約などで複数定義すること。または同名の関数の集合">オーバーロード</a>が<code>function(F&&)</code>に変更された</li>
</ul>
</li>
</ul></div>
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