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 <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