ceph/src/Beast/include/beast/core/detail/is_call_possible.hpp

   1 //
   2 // Copyright (c) 2013-2017 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
   8 #ifndef BEAST_DETAIL_IS_CALL_POSSIBLE_HPP
   9 #define BEAST_DETAIL_IS_CALL_POSSIBLE_HPP
  10
  11 #include <type_traits>
  12
  13 namespace beast {
  14 namespace detail {
  15
  16 template<class R, class C, class ...A>
  17 auto
  18 is_call_possible_test(C&& c, int, A&& ...a)
  19     -> decltype(std::is_convertible<
  20         decltype(c(a...)), R>::value ||
  21             std::is_same<R, void>::value,
  22                 std::true_type());
  23
  24 template<class R, class C, class ...A>
  25 std::false_type
  26 is_call_possible_test(C&& c, long, A&& ...a);
  27
  28 /** Metafunction returns `true` if F callable as R(A...)
  29
  30     Example:
  31
  32     @code
  33         is_call_possible<T, void(std::string)>
  34     @endcode
  35 */
  36 /** @{ */
  37 template<class C, class F>
  38 struct is_call_possible
  39     : std::false_type
  40 {
  41 };
  42
  43 template<class C, class R, class ...A>
  44 struct is_call_possible<C, R(A...)>
  45     : decltype(is_call_possible_test<R>(
  46         std::declval<C>(), 1, std::declval<A>()...))
  47 {
  48 };
  49 /** @} */
  50
  51 } // detail
  52 } // beast
  53
  54 #endif