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
18namespace 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 {
33 compound_modifier()
34 : Current(), New() {}
35
36 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 {
46 compound_modifier()
47 : Current() {}
48
49 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 {
57 compound_modifier()
58 : New() {}
59
60 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
95 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
102 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>
109 op(Tag tag, Modifiers modifiers, mpl::true_) const
110 {
111 return compound_modifier<Modifiers, Tag>(modifiers, tag);
112 }
113 };
114}}
115
116#endif
117

source code of boost/libs/spirit/include/boost/spirit/home/support/modify.hpp