1 | |
2 | // (C) Copyright Edward Diener 2011,2012,2013 |
3 | // Use, modification and distribution are subject to the Boost Software License, |
4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
5 | // http://www.boost.org/LICENSE_1_0.txt). |
6 | |
7 | #if !defined(BOOST_TTI_HAS_TYPE_HPP) |
8 | #define BOOST_TTI_HAS_TYPE_HPP |
9 | |
10 | #include <boost/config.hpp> |
11 | #include <boost/preprocessor/cat.hpp> |
12 | #include <boost/tti/gen/has_type_gen.hpp> |
13 | #include <boost/tti/gen/namespace_gen.hpp> |
14 | #include <boost/tti/detail/dtype.hpp> |
15 | #include <boost/tti/detail/ddeftype.hpp> |
16 | |
17 | /* |
18 | |
19 | The succeeding comments in this file are in doxygen format. |
20 | |
21 | */ |
22 | |
23 | /** \file |
24 | */ |
25 | |
26 | /** |
27 | |
28 | BOOST_TTI_TRAIT_HAS_TYPE is a macro which expands to a metafunction. |
29 | The metafunction tests whether an inner type with a particular name exists |
30 | and, optionally, whether a lambda expression invoked with the inner type |
31 | is true or not. |
32 | |
33 | trait = the name of the metafunction within the tti namespace. |
34 | |
35 | name = the name of the inner type. |
36 | |
37 | generates a metafunction called "trait" where 'trait' is the macro parameter. |
38 | |
39 | template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U> |
40 | struct trait |
41 | { |
42 | static const value = unspecified; |
43 | typedef mpl::bool_<true-or-false> type; |
44 | }; |
45 | |
46 | The metafunction types and return: |
47 | |
48 | BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'. |
49 | |
50 | BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type. |
51 | If specified it is an MPL lambda expression which is invoked |
52 | with the inner type found and must return a constant boolean |
53 | value. |
54 | |
55 | returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified. |
56 | |
57 | If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' type |
58 | exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false. |
59 | |
60 | If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' type exists |
61 | within the enclosing type BOOST_TTI_TP_T and the lambda expression as specified |
62 | by BOOST_TTI_TP_U, invoked by passing the actual inner type of 'name', returns |
63 | a 'value' of true; otherwise 'value' is false. |
64 | |
65 | The action taken with BOOST_TTI_TP_U occurs only when the 'name' type exists |
66 | within the enclosing type BOOST_TTI_TP_T. |
67 | |
68 | Example usage: |
69 | |
70 | BOOST_TTI_TRAIT_HAS_TYPE(LookFor,MyType) generates the metafunction LookFor in the current scope |
71 | to look for an inner type called MyType. |
72 | |
73 | LookFor<EnclosingType>::value is true if MyType is an inner type of EnclosingType, otherwise false. |
74 | |
75 | LookFor<EnclosingType,ALambdaExpression>::value is true if MyType is an inner type of EnclosingType |
76 | and invoking ALambdaExpression with the inner type returns a value of true, otherwise false. |
77 | |
78 | A popular use of the optional MPL lambda expression is to check whether the type found is the same |
79 | as another type, when the type found is a typedef. In that case our example would be: |
80 | |
81 | LookFor<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner type |
82 | of EnclosingType and is the same type as SomeOtherType. |
83 | |
84 | */ |
85 | #define BOOST_TTI_TRAIT_HAS_TYPE(trait,name) \ |
86 | BOOST_TTI_DETAIL_TRAIT_HAS_TYPE(trait,name) \ |
87 | template \ |
88 | < \ |
89 | class BOOST_TTI_TP_T, \ |
90 | class BOOST_TTI_TP_U = BOOST_TTI_NAMESPACE::detail::deftype \ |
91 | > \ |
92 | struct trait \ |
93 | { \ |
94 | typedef typename \ |
95 | BOOST_PP_CAT(trait,_detail_type)<BOOST_TTI_TP_T,BOOST_TTI_TP_U>::type type; \ |
96 | BOOST_STATIC_CONSTANT(bool,value=type::value); \ |
97 | }; \ |
98 | /**/ |
99 | |
100 | /** |
101 | |
102 | BOOST_TTI_HAS_TYPE is a macro which expands to a metafunction. |
103 | The metafunction tests whether an inner type with a particular name exists |
104 | and, optionally, whether a lambda expression invoked with the inner type |
105 | is true or not. |
106 | |
107 | name = the name of the inner type. |
108 | |
109 | generates a metafunction called "has_type_'name'" where 'name' is the macro parameter. |
110 | |
111 | template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U> |
112 | struct has_type_'name' |
113 | { |
114 | static const value = unspecified; |
115 | typedef mpl::bool_<true-or-false> type; |
116 | }; |
117 | |
118 | The metafunction types and return: |
119 | |
120 | BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'. |
121 | |
122 | BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type. |
123 | If specified it is an MPL lambda expression which is invoked |
124 | with the inner type found and must return a constant boolean |
125 | value. |
126 | |
127 | returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified. |
128 | |
129 | If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' type |
130 | exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false. |
131 | |
132 | If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' type exists |
133 | within the enclosing type BOOST_TTI_TP_T and the lambda expression as specified |
134 | by BOOST_TTI_TP_U, invoked by passing the actual inner type of 'name', returns |
135 | a 'value' of true; otherwise 'value' is false. |
136 | |
137 | The action taken with BOOST_TTI_TP_U occurs only when the 'name' type exists |
138 | within the enclosing type BOOST_TTI_TP_T. |
139 | |
140 | Example usage: |
141 | |
142 | BOOST_TTI_HAS_TYPE(MyType) generates the metafunction has_type_MyType in the current scope |
143 | to look for an inner type called MyType. |
144 | |
145 | has_type_MyType<EnclosingType>::value is true if MyType is an inner type of EnclosingType, otherwise false. |
146 | |
147 | has_type_MyType<EnclosingType,ALambdaExpression>::value is true if MyType is an inner type of EnclosingType |
148 | and invoking ALambdaExpression with the inner type returns a value of true, otherwise false. |
149 | |
150 | A popular use of the optional MPL lambda expression is to check whether the type found is the same |
151 | as another type, when the type found is a typedef. In that case our example would be: |
152 | |
153 | has_type_MyType<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner type |
154 | of EnclosingType and is the same type as SomeOtherType. |
155 | |
156 | */ |
157 | #define BOOST_TTI_HAS_TYPE(name) \ |
158 | BOOST_TTI_TRAIT_HAS_TYPE \ |
159 | ( \ |
160 | BOOST_TTI_HAS_TYPE_GEN(name), \ |
161 | name \ |
162 | ) \ |
163 | /**/ |
164 | |
165 | #endif // BOOST_TTI_HAS_TYPE_HPP |
166 | |