1 // Copyright David Abrahams 2005.
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 #ifndef BOOST_PARAMETER_AUX_RESULT_OF0_DWA2005511_HPP
7 #define BOOST_PARAMETER_AUX_RESULT_OF0_DWA2005511_HPP
8 
9 #include <boost/parameter/aux_/use_default_tag.hpp>
10 #include <boost/parameter/config.hpp>
11 #include <boost/utility/result_of.hpp>
12 
13 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
14 #include <boost/mp11/utility.hpp>
15 #include <type_traits>
16 #else
17 #include <boost/mpl/if.hpp>
18 #include <boost/type_traits/is_void.hpp>
19 #endif
20 
21 namespace boost { namespace parameter { namespace aux {
22 
23     // A metafunction returning the result of invoking
24     // a nullary function object of the given type.
25     template <typename F>
26     class result_of0
27     {
28 #if defined(BOOST_NO_RESULT_OF)
29         typedef typename F::result_type result_of_F;
30 #else
31         typedef typename ::boost::result_of<F()>::type result_of_F;
32 #endif
33 
34      public:
35 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
36         using type = ::boost::mp11::mp_if<
37             ::std::is_void<result_of_F>
38 #else
39         typedef typename ::boost::mpl::if_<
40             ::boost::is_void<result_of_F>
41 #endif
42           , ::boost::parameter::aux::use_default_tag
43           , result_of_F
44 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
45         >;
46 #else
47         >::type type;
48 #endif
49     };
50 }}} // namespace boost::parameter::aux
51 
52 #endif  // include guard
53 
54