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 <boost/asio/async_result.hpp> 14 #include <boost/type_traits/make_void.hpp> 15 #include <type_traits> 16 #include <utility> 17 18 namespace boost { 19 namespace beast { 20 namespace detail { 21 22 template<class R, class C, class ...A> 23 auto 24 is_invocable_test(C&& c, int, A&& ...a) 25 -> decltype(std::is_convertible< 26 decltype(c(std::forward<A>(a)...)), R>::value || 27 std::is_same<R, void>::value, 28 std::true_type()); 29 30 template<class R, class C, class ...A> 31 std::false_type 32 is_invocable_test(C&& c, long, A&& ...a); 33 34 /** Metafunction returns `true` if F callable as R(A...) 35 36 Example: 37 38 @code 39 is_invocable<T, void(std::string)>::value 40 @endcode 41 */ 42 /** @{ */ 43 template<class C, class F> 44 struct is_invocable : std::false_type 45 { 46 }; 47 48 template<class C, class R, class ...A> 49 struct is_invocable<C, R(A...)> 50 : decltype(is_invocable_test<R>( 51 std::declval<C>(), 1, std::declval<A>()...)) 52 { 53 }; 54 /** @} */ 55 56 template<class CompletionToken, class Signature, class = void> 57 struct is_completion_token_for : std::false_type 58 { 59 }; 60 61 struct any_initiation 62 { 63 template<class...AnyArgs> 64 void operator()(AnyArgs&&...); 65 }; 66 67 template<class CompletionToken, class R, class...Args> 68 struct is_completion_token_for< 69 CompletionToken, R(Args...), boost::void_t<decltype( 70 boost::asio::async_initiate<CompletionToken, R(Args...)>( 71 any_initiation(), std::declval<CompletionToken&>()) 72 )>> : std::true_type 73 { 74 }; 75 76 } // detail 77 } // beast 78 } // boost 79 80 #endif 81