1 /*=============================================================================
2   Copyright (c) 2001-2011 Joel de Guzman
3   http://spirit.sourceforge.net/
4 
5   Distributed under the Boost Software License, Version 1.0. (See accompanying
6   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7 =============================================================================*/
8 #ifndef BOOST_SPIRIT_MODIFY_OCTOBER_25_2008_0142PM
9 #define BOOST_SPIRIT_MODIFY_OCTOBER_25_2008_0142PM
10 
11 #if defined(_MSC_VER)
12 #pragma once
13 #endif
14 
15 #include <boost/type_traits/is_base_of.hpp>
16 #include <boost/spirit/home/support/unused.hpp>
17 
18 namespace boost { namespace spirit
19 {
20     template <typename Domain, typename T, typename Enable = void>
21     struct is_modifier_directive;
22 
23     // Testing if a modifier set includes a modifier T involves
24     // checking for inheritance (i.e. Modifiers is derived from T)
25     template <typename Modifiers, typename T>
26     struct has_modifier
27         : is_base_of<T, Modifiers> {};
28 
29     // Adding modifiers is done using multi-inheritance
30     template <typename Current, typename New, typename Enable = void>
31     struct compound_modifier : Current, New
32     {
compound_modifierboost::spirit::compound_modifier33         compound_modifier()
34           : Current(), New() {}
35 
compound_modifierboost::spirit::compound_modifier36         compound_modifier(Current const& current, New const& new_)
37           : Current(current), New(new_) {}
38     };
39 
40     // Don't add if New is already in Current
41     template <typename Current, typename New>
42     struct compound_modifier<
43         Current, New, typename enable_if<has_modifier<Current, New> >::type>
44       : Current
45     {
compound_modifierboost::spirit::compound_modifier46         compound_modifier()
47           : Current() {}
48 
compound_modifierboost::spirit::compound_modifier49         compound_modifier(Current const& current, New const&)
50           : Current(current) {}
51     };
52 
53     // Special case if Current is unused_type
54     template <typename New, typename Enable>
55     struct compound_modifier<unused_type, New, Enable> : New
56     {
compound_modifierboost::spirit::compound_modifier57         compound_modifier()
58           : New() {}
59 
compound_modifierboost::spirit::compound_modifier60         compound_modifier(unused_type, New const& new_)
61           : New(new_) {}
62     };
63 
64     // Domains may specialize this modify metafunction to allow
65     // directives to add information to the Modifier template
66     // parameter that is passed to the make_component metafunction.
67     // By default, we return the modifiers untouched
68     template <typename Domain, typename Enable = void>
69     struct modify
70     {
71         typedef void proto_is_callable_;
72 
73         template <typename Sig>
74         struct result;
75 
76         template <typename This, typename Tag, typename Modifiers>
77         struct result<This(Tag, Modifiers)>
78         {
79             typedef typename remove_const<
80                 typename remove_reference<Tag>::type>::type
81             tag_type;
82             typedef typename remove_const<
83                 typename remove_reference<Modifiers>::type>::type
84             modifiers_type;
85 
86             typedef typename mpl::if_<
87                 is_modifier_directive<Domain, tag_type>
88               , compound_modifier<modifiers_type, tag_type>
89               , Modifiers>::type
90             type;
91         };
92 
93         template <typename Tag, typename Modifiers>
94         typename result<modify(Tag, Modifiers)>::type
operator ()boost::spirit::modify95         operator()(Tag tag, Modifiers modifiers) const
96         {
97             return op(tag, modifiers, is_modifier_directive<Domain, Tag>());
98         }
99 
100         template <typename Tag, typename Modifiers>
101         Modifiers
opboost::spirit::modify102         op(Tag /*tag*/, Modifiers modifiers, mpl::false_) const
103         {
104             return modifiers;
105         }
106 
107         template <typename Tag, typename Modifiers>
108         compound_modifier<Modifiers, Tag>
opboost::spirit::modify109         op(Tag tag, Modifiers modifiers, mpl::true_) const
110         {
111             return compound_modifier<Modifiers, Tag>(modifiers, tag);
112         }
113     };
114 }}
115 
116 #endif
117