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
15namespace boost
16{
17
18namespace type_traits_detail
19{
20
21// mp_valid
22// implementation by Bruno Dutra (by the name is_evaluable)
23
24template<template<class...> class F, class... T>
25struct 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
36template<template<class...> class F, class... T>
37using mp_valid = typename mp_valid_impl<F, T...>::type;
38
39// mp_defer
40
41struct mp_empty
42{
43};
44
45template<template<class...> class F, class... T> struct mp_defer_impl
46{
47 using type = F<T...>;
48};
49
50template<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
57

source code of include/boost/type_traits/detail/mp_defer.hpp