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