1 | // Copyright Daniel Wallin 2006. |
2 | // Copyright Cromwell D. Enage 2017. |
3 | // Distributed under the Boost Software License, Version 1.0. |
4 | // (See accompanying file LICENSE_1_0.txt or copy at |
5 | // http://www.boost.org/LICENSE_1_0.txt) |
6 | |
7 | #ifndef BOOST_PARAMETER_TEMPLATE_KEYWORD_HPP |
8 | #define BOOST_PARAMETER_TEMPLATE_KEYWORD_HPP |
9 | |
10 | #include <boost/parameter/aux_/template_keyword.hpp> |
11 | #include <boost/parameter/config.hpp> |
12 | |
13 | #if defined(BOOST_PARAMETER_CAN_USE_MP11) |
14 | #include <boost/mp11/integral.hpp> |
15 | #include <boost/mp11/utility.hpp> |
16 | #include <type_traits> |
17 | #else |
18 | #include <boost/mpl/bool.hpp> |
19 | #include <boost/mpl/if.hpp> |
20 | #include <boost/mpl/eval_if.hpp> |
21 | #include <boost/mpl/identity.hpp> |
22 | #include <boost/type_traits/add_lvalue_reference.hpp> |
23 | #include <boost/type_traits/is_function.hpp> |
24 | #include <boost/type_traits/is_array.hpp> |
25 | #endif |
26 | |
27 | namespace boost { namespace parameter { |
28 | |
29 | template <typename Tag, typename T> |
30 | struct template_keyword : ::boost::parameter::aux::template_keyword_base |
31 | { |
32 | typedef Tag key_type; |
33 | typedef T value_type; |
34 | |
35 | // reference is needed for two reasons: |
36 | // |
37 | // 1. It is used in the body of arg_list<...> |
38 | // |
39 | // 2. It is the result of binding<...>, which we mistakenly told |
40 | // people to use instead of value_type<...> to access named |
41 | // template parameters |
42 | // |
43 | // It used to be that reference == value_type, but that broke when |
44 | // the argument was a function or array type, because various |
45 | // arg_list functions return reference. |
46 | // |
47 | // Simply making reference == value_type& would break all the |
48 | // legacy code that uses binding<...> to access named template |
49 | // parameters. -- David Abrahams |
50 | #if defined(BOOST_PARAMETER_CAN_USE_MP11) |
51 | using reference = typename ::boost::mp11::mp_eval_if< |
52 | ::boost::mp11::mp_if< |
53 | ::std::is_function<value_type> |
54 | , ::boost::mp11::mp_true |
55 | , ::std::is_array<value_type> |
56 | > |
57 | , ::std::add_lvalue_reference<value_type> |
58 | , ::boost::mp11::mp_identity |
59 | , value_type |
60 | >::type; |
61 | #else |
62 | typedef typename ::boost::mpl::eval_if< |
63 | typename ::boost::mpl::if_< |
64 | ::boost::is_function<value_type> |
65 | , ::boost::mpl::true_ |
66 | , ::boost::is_array<value_type> |
67 | >::type |
68 | , ::boost::add_lvalue_reference<value_type> |
69 | , ::boost::mpl::identity<value_type> |
70 | >::type reference; |
71 | #endif // BOOST_PARAMETER_CAN_USE_MP11 |
72 | }; |
73 | }} // namespace boost::parameter |
74 | |
75 | #define BOOST_PARAMETER_TEMPLATE_KEYWORD(name) \ |
76 | namespace tag \ |
77 | { \ |
78 | struct name; \ |
79 | } \ |
80 | template <typename T> \ |
81 | struct name : ::boost::parameter::template_keyword<tag::name,T> \ |
82 | { \ |
83 | }; |
84 | /**/ |
85 | |
86 | #endif // include guard |
87 | |
88 | |