ceph/src/boost/boost/poly_collection/detail/is_invocable.hpp

   1 /* Copyright 2016-2017 Joaquin M Lopez Munoz.
   2  * Distributed under the Boost Software License, Version 1.0.
   3  * (See accompanying file LICENSE_1_0.txt or copy at
   4  * http://www.boost.org/LICENSE_1_0.txt)
   5  *
   6  * See http://www.boost.org/libs/poly_collection for library home page.
   7  */
   8
   9 #ifndef BOOST_POLY_COLLECTION_DETAIL_IS_INVOCABLE_HPP
  10 #define BOOST_POLY_COLLECTION_DETAIL_IS_INVOCABLE_HPP
  11
  12 #if defined(_MSC_VER)
  13 #pragma once
  14 #endif
  15
  16 #include <functional>
  17 #include <type_traits>
  18
  19 /* technique explained at
  20  * http://bannalia.blogspot.com/2016/09/compile-time-checking-existence-of.html
  21  */
  22
  23 namespace boost{
  24 namespace poly_collection{
  25 namespace detail{
  26 namespace is_invocable_fallback{
  27
  28 template <typename F,typename... Args>
  29 struct is_invocable:
  30   std::is_constructible<
  31     std::function<void(Args...)>,
  32     std::reference_wrapper<typename std::remove_reference<F>::type>
  33   >
  34 {};
  35
  36 template <typename R,typename F,typename... Args>
  37 struct is_invocable_r:
  38   std::is_constructible<
  39     std::function<R(Args...)>,
  40     std::reference_wrapper<typename std::remove_reference<F>::type>
  41   >
  42 {};
  43
  44 struct hook{};
  45
  46 }}}}
  47
  48 namespace std{
  49
  50 template<>
  51 struct is_void< ::boost::poly_collection::detail::is_invocable_fallback::hook>:
  52   std::false_type
  53 {
  54   template<typename F,typename... Args>
  55   static constexpr bool is_invocable_f()
  56   {
  57     using namespace ::boost::poly_collection::detail::is_invocable_fallback;
  58     return is_invocable<F,Args...>::value;
  59   }
  60
  61   template<typename R,typename F,typename... Args>
  62   static constexpr bool is_invocable_r_f()
  63   {
  64     using namespace ::boost::poly_collection::detail::is_invocable_fallback;
  65     return is_invocable_r<R,F,Args...>::value;
  66   }
  67 };
  68
  69 } /* namespace std */
  70
  71 namespace boost{
  72
  73 namespace poly_collection{
  74
  75 namespace detail{
  76
  77 template<typename F,typename... Args>
  78 struct is_invocable:std::integral_constant<
  79   bool,
  80   std::is_void<is_invocable_fallback::hook>::template
  81     is_invocable_f<F,Args...>()
  82 >{};
  83
  84 template<typename R,typename F,typename... Args>
  85 struct is_invocable_r:std::integral_constant<
  86   bool,
  87   std::is_void<is_invocable_fallback::hook>::template
  88     is_invocable_r_f<R,F,Args...>()
  89 >{};
  90
  91 } /* namespace poly_collection::detail */
  92
  93 } /* namespace poly_collection */
  94
  95 } /* namespace boost */
  96
  97 #endif