ceph/src/boost/boost/beast/core/detail/is_invocable.hpp

   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