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

source code of boost/boost/tti/has_type.hpp