1 // Copyright David Abrahams, Daniel Wallin 2003.
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_REQUIRED_HPP
7 #define BOOST_PARAMETER_REQUIRED_HPP
8 
9 #include <boost/parameter/aux_/use_default.hpp>
10 
11 namespace boost { namespace parameter {
12 
13     // This metafunction can be used to describe the treatment of particular
14     // named parameters for the purposes of overload elimination with SFINAE,
15     // by placing specializations in the parameters<...> list.  In order for
16     // a treated function to participate in overload resolution:
17     //
18     //   - all keyword tags wrapped in required<...> must have a matching
19     //     actual argument
20     //
21     //   - The actual argument type matched by every keyword tag
22     //     associated with a predicate must satisfy that predicate
23     template <
24         typename Tag
25       , typename Predicate = ::boost::parameter::aux::use_default
26     >
27     struct required
28     {
29         typedef Tag key_type;
30         typedef Predicate predicate;
31     };
32 }}
33 
34 #include <boost/parameter/config.hpp>
35 
36 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
37 #include <boost/mp11/integral.hpp>
38 #else
39 #include <boost/mpl/bool.hpp>
40 #endif
41 
42 namespace boost { namespace parameter { namespace aux {
43 
44     template <typename T>
45     struct is_required
46 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
47       : ::boost::mp11::mp_false
48 #else
49       : ::boost::mpl::false_
50 #endif
51     {
52     };
53 
54     template <typename Tag, typename Predicate>
55     struct is_required< ::boost::parameter::required<Tag,Predicate> >
56 #if defined(BOOST_PARAMETER_CAN_USE_MP11)
57       : ::boost::mp11::mp_true
58 #else
59       : ::boost::mpl::true_
60 #endif
61     {
62     };
63 }}} // namespace boost::parameter::aux
64 
65 #endif  // include guard
66 
67