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