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
11namespace 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
42namespace 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

source code of boost/libs/parameter/include/boost/parameter/required.hpp