1 | /* Copyright 2003-2015 Joaquin M Lopez Munoz. |
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 | * See http://www.boost.org/libs/multi_index for library home page. |
7 | */ |
8 | |
9 | #ifndef BOOST_MULTI_INDEX_IDENTITY_HPP |
10 | #define BOOST_MULTI_INDEX_IDENTITY_HPP |
11 | |
12 | #if defined(_MSC_VER) |
13 | #pragma once |
14 | #endif |
15 | |
16 | #include <boost/config.hpp> |
17 | #include <boost/detail/workaround.hpp> |
18 | #include <boost/mpl/if.hpp> |
19 | #include <boost/multi_index/identity_fwd.hpp> |
20 | #include <boost/type_traits/is_const.hpp> |
21 | #include <boost/type_traits/remove_const.hpp> |
22 | #include <boost/utility/enable_if.hpp> |
23 | |
24 | #if !defined(BOOST_NO_SFINAE) |
25 | #include <boost/type_traits/is_convertible.hpp> |
26 | #endif |
27 | |
28 | namespace boost{ |
29 | |
30 | template<class Type> class reference_wrapper; /* fwd decl. */ |
31 | |
32 | namespace multi_index{ |
33 | |
34 | namespace detail{ |
35 | |
36 | /* identity is a do-nothing key extractor that returns the [const] Type& |
37 | * object passed. |
38 | * Additionally, identity is overloaded to support referece_wrappers |
39 | * of Type and "chained pointers" to Type's. By chained pointer to Type we |
40 | * mean a type P such that, given a p of type P |
41 | * *...n...*x is convertible to Type&, for some n>=1. |
42 | * Examples of chained pointers are raw and smart pointers, iterators and |
43 | * arbitrary combinations of these (vg. Type** or unique_ptr<Type*>.) |
44 | */ |
45 | |
46 | template<typename Type> |
47 | struct const_identity_base |
48 | { |
49 | typedef Type result_type; |
50 | |
51 | template<typename ChainedPtr> |
52 | |
53 | #if !defined(BOOST_NO_SFINAE) |
54 | typename disable_if<is_convertible<const ChainedPtr&,Type&>,Type&>::type |
55 | #else |
56 | Type& |
57 | #endif |
58 | |
59 | operator()(const ChainedPtr& x)const |
60 | { |
61 | return operator()(*x); |
62 | } |
63 | |
64 | Type& operator()(Type& x)const |
65 | { |
66 | return x; |
67 | } |
68 | |
69 | Type& operator()(const reference_wrapper<Type>& x)const |
70 | { |
71 | return x.get(); |
72 | } |
73 | |
74 | Type& operator()( |
75 | const reference_wrapper<typename remove_const<Type>::type>& x |
76 | |
77 | #if BOOST_WORKAROUND(BOOST_MSVC,==1310) |
78 | /* http://lists.boost.org/Archives/boost/2015/10/226135.php */ |
79 | ,int=0 |
80 | #endif |
81 | |
82 | )const |
83 | { |
84 | return x.get(); |
85 | } |
86 | }; |
87 | |
88 | template<typename Type> |
89 | struct non_const_identity_base |
90 | { |
91 | typedef Type result_type; |
92 | |
93 | /* templatized for pointer-like types */ |
94 | |
95 | template<typename ChainedPtr> |
96 | |
97 | #if !defined(BOOST_NO_SFINAE) |
98 | typename disable_if< |
99 | is_convertible<const ChainedPtr&,const Type&>,Type&>::type |
100 | #else |
101 | Type& |
102 | #endif |
103 | |
104 | operator()(const ChainedPtr& x)const |
105 | { |
106 | return operator()(*x); |
107 | } |
108 | |
109 | const Type& operator()(const Type& x)const |
110 | { |
111 | return x; |
112 | } |
113 | |
114 | Type& operator()(Type& x)const |
115 | { |
116 | return x; |
117 | } |
118 | |
119 | const Type& operator()(const reference_wrapper<const Type>& x)const |
120 | { |
121 | return x.get(); |
122 | } |
123 | |
124 | Type& operator()(const reference_wrapper<Type>& x)const |
125 | { |
126 | return x.get(); |
127 | } |
128 | }; |
129 | |
130 | } /* namespace multi_index::detail */ |
131 | |
132 | template<class Type> |
133 | struct identity: |
134 | mpl::if_c< |
135 | is_const<Type>::value, |
136 | detail::const_identity_base<Type>,detail::non_const_identity_base<Type> |
137 | >::type |
138 | { |
139 | }; |
140 | |
141 | } /* namespace multi_index */ |
142 | |
143 | } /* namespace boost */ |
144 | |
145 | #endif |
146 | |