1 // 2 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com) 3 // 4 // Distributed under the Boost Software License, Version 1.0. (See accompanying 5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6 // 7 // Official repository: https://github.com/boostorg/beast 8 // 9 10 #ifndef BOOST_BEAST_DETAIL_IS_INVOCABLE_HPP 11 #define BOOST_BEAST_DETAIL_IS_INVOCABLE_HPP 12 13 #include <type_traits> 14 #include <utility> 15 16 namespace boost { 17 namespace beast { 18 namespace detail { 19 20 template<class R, class C, class ...A> 21 auto 22 is_invocable_test(C&& c, int, A&& ...a) 23 -> decltype(std::is_convertible< 24 decltype(c(std::forward<A>(a)...)), R>::value || 25 std::is_same<R, void>::value, 26 std::true_type()); 27 28 template<class R, class C, class ...A> 29 std::false_type 30 is_invocable_test(C&& c, long, A&& ...a); 31 32 /** Metafunction returns `true` if F callable as R(A...) 33 34 Example: 35 36 @code 37 is_invocable<T, void(std::string)>::value 38 @endcode 39 */ 40 /** @{ */ 41 template<class C, class F> 42 struct is_invocable : std::false_type 43 { 44 }; 45 46 template<class C, class R, class ...A> 47 struct is_invocable<C, R(A...)> 48 : decltype(is_invocable_test<R>( 49 std::declval<C>(), 1, std::declval<A>()...)) 50 { 51 }; 52 /** @} */ 53 54 } // detail 55 } // beast 56 } // boost 57 58 #endif 59