ceph/src/boost/libs/type_traits/include/boost/type_traits/detail/mp_defer.hpp

   1 #ifndef BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED
   2 #define BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED
   3
   4 //
   5 //  Copyright 2015 Peter Dimov
   6 //
   7 //  Distributed under the Boost Software License, Version 1.0.
   8 //  See accompanying file LICENSE_1_0.txt or copy at
   9 //  http://www.boost.org/LICENSE_1_0.txt
  10 //
  11
  12 #include <boost/type_traits/integral_constant.hpp>
  13 #include <boost/type_traits/conditional.hpp>
  14
  15 namespace boost
  16 {
  17
  18 namespace type_traits_detail
  19 {
  20
  21 // mp_valid
  22 // implementation by Bruno Dutra (by the name is_evaluable)
  23
  24 template<template<class...> class F, class... T>
  25 struct mp_valid_impl
  26 {
  27     template<template<class...> class G, class = G<T...>>
  28     static boost::true_type check_s(int);
  29
  30     template<template<class...> class>
  31     static boost::false_type check_s(...);
  32
  33     using type = decltype(check_s<F>(0));
  34 };
  35
  36 template<template<class...> class F, class... T>
  37 using mp_valid = typename mp_valid_impl<F, T...>::type;
  38
  39 // mp_defer
  40
  41 struct mp_empty
  42 {
  43 };
  44
  45 template<template<class...> class F, class... T> struct mp_defer_impl
  46 {
  47     using type = F<T...>;
  48 };
  49
  50 template<template<class...> class F, class... T> using mp_defer = typename boost::conditional<mp_valid<F, T...>::value, mp_defer_impl<F, T...>, mp_empty>::type;
  51
  52 } // namespace type_traits_detail
  53
  54 } // namespace boost
  55
  56 #endif // #ifndef BOOST_TYPE_TRAITS_DETAIL_MP_DEFER_HPP_INCLUDED