1/*=============================================================================
2 Copyright (c) 2001-2014 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#if !defined(BOOST_SPIRIT_X3_CONTEXT_JAN_4_2012_1215PM)
9#define BOOST_SPIRIT_X3_CONTEXT_JAN_4_2012_1215PM
10
11#include <boost/spirit/home/x3/support/unused.hpp>
12#include <boost/mpl/identity.hpp>
13
14namespace boost { namespace spirit { namespace x3
15{
16 template <typename ID, typename T, typename Next = unused_type>
17 struct context
18 {
19 context(T& val, Next const& next)
20 : val(val), next(next) {}
21
22 T& get(mpl::identity<ID>) const
23 {
24 return val;
25 }
26
27 template <typename ID_>
28 decltype(auto) get(ID_ id) const
29 {
30 return next.get(id);
31 }
32
33 T& val;
34 Next const& next;
35 };
36
37 template <typename ID, typename T>
38 struct context<ID, T, unused_type>
39 {
40 context(T& val)
41 : val(val) {}
42
43 context(T& val, unused_type)
44 : val(val) {}
45
46 T& get(mpl::identity<ID>) const
47 {
48 return val;
49 }
50
51 template <typename ID_>
52 unused_type get(ID_) const
53 {
54 return {};
55 }
56
57 T& val;
58 };
59
60 template <typename Tag, typename Context>
61 inline decltype(auto) get(Context const& context)
62 {
63 return context.get(mpl::identity<Tag>());
64 }
65
66 template <typename ID, typename T, typename Next>
67 inline context<ID, T, Next> make_context(T& val, Next const& next)
68 {
69 return { val, next };
70 }
71
72 template <typename ID, typename T>
73 inline context<ID, T> make_context(T& val)
74 {
75 return { val };
76 }
77
78 namespace detail
79 {
80 template <typename ID, typename T, typename Next, typename FoundVal>
81 inline Next const&
82 make_unique_context(T& /* val */, Next const& next, FoundVal&)
83 {
84 return next;
85 }
86
87 template <typename ID, typename T, typename Next>
88 inline context<ID, T, Next>
89 make_unique_context(T& val, Next const& next, unused_type)
90 {
91 return { val, next };
92 }
93 }
94
95 template <typename ID, typename T, typename Next>
96 inline auto
97 make_unique_context(T& val, Next const& next)
98 {
99 return detail::make_unique_context<ID>(val, next, x3::get<ID>(next));
100 }
101}}}
102
103#endif
104

source code of boost/libs/spirit/include/boost/spirit/home/x3/support/context.hpp