1
2// (C) Copyright Edward Diener 2019
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_UNION_HPP)
8#define BOOST_TTI_HAS_UNION_HPP
9
10#include <boost/config.hpp>
11#include <boost/preprocessor/cat.hpp>
12#include <boost/tti/gen/has_union_gen.hpp>
13#include <boost/tti/gen/namespace_gen.hpp>
14#include <boost/tti/detail/dunion.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/// A macro which expands to a metafunction which tests whether an inner union with a particular name exists.
27/**
28
29 BOOST_TTI_TRAIT_HAS_UNION is a macro which expands to a metafunction.
30 The metafunction tests whether an inner union with a particular name exists
31 and, optionally, whether an MPL lambda expression invoked with the inner union
32 is true or not. The macro takes the form of BOOST_TTI_TRAIT_HAS_UNION(trait,name) where
33
34 trait = the name of the metafunction <br/>
35 name = the name of the inner union.
36
37 BOOST_TTI_TRAIT_HAS_UNION generates a metafunction called "trait" where 'trait' is the macro parameter.
38
39 @code
40
41 template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U>
42 struct trait
43 {
44 static const value = unspecified;
45 typedef mpl::bool_<true-or-false> type;
46 };
47
48 The metafunction types and return:
49
50 BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'.
51 The enclosing type can be a class, struct, or union.
52
53 BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type.
54 If specified it is an MPL lambda expression which is invoked
55 with the inner union found and must return a constant boolean
56 value.
57
58 returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified.
59
60 If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' union
61 exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false.
62
63 If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' union exists
64 within the enclosing type BOOST_TTI_TP_T and the MPL lambda expression as specified
65 by BOOST_TTI_TP_U, invoked by passing the actual inner union of 'name', returns
66 a 'value' of true; otherwise 'value' is false.
67
68 The action taken with BOOST_TTI_TP_U occurs only when the 'name' union exists
69 within the enclosing type BOOST_TTI_TP_T.
70
71 @endcode
72
73 Example usage:
74
75 @code
76
77 BOOST_TTI_TRAIT_HAS_UNION(LookFor,MyType) generates the metafunction LookFor in the current scope
78 to look for an inner union called MyType.
79
80 LookFor<EnclosingType>::value is true if MyType is an inner union of EnclosingType, otherwise false.
81
82 LookFor<EnclosingType,ALambdaExpression>::value is true if MyType is an inner union of EnclosingType
83 and invoking ALambdaExpression with the inner union returns a value of true, otherwise false.
84
85 A popular use of the optional MPL lambda expression is to check whether the union found is the same
86 as another type, when the union found is a typedef. In that case our example would be:
87
88 LookFor<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner union
89 of EnclosingType and is the same type as SomeOtherType.
90
91 @endcode
92
93*/
94#define BOOST_TTI_TRAIT_HAS_UNION(trait,name) \
95 BOOST_TTI_DETAIL_TRAIT_HAS_UNION(trait,name) \
96 template \
97 < \
98 class BOOST_TTI_TP_T, \
99 class BOOST_TTI_TP_U = BOOST_TTI_NAMESPACE::detail::deftype \
100 > \
101 struct trait \
102 { \
103 typedef typename \
104 BOOST_PP_CAT(trait,_detail_union)<BOOST_TTI_TP_T,BOOST_TTI_TP_U>::type type; \
105 BOOST_STATIC_CONSTANT(bool,value=type::value); \
106 }; \
107/**/
108
109/// A macro which expands to a metafunction which tests whether an inner union with a particular name exists.
110/**
111
112 BOOST_TTI_HAS_UNION is a macro which expands to a metafunction.
113 The metafunction tests whether an inner union with a particular name exists
114 and, optionally, whether an MPL lambda expression invoked with the inner union
115 is true or not. The macro takes the form of BOOST_TTI_HAS_UNION(name) where
116
117 name = the name of the inner union.
118
119 BOOST_TTI_HAS_UNION generates a metafunction called "has_union_'name'" where 'name' is the macro parameter.
120
121 @code
122
123 template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U>
124 struct has_union_'name'
125 {
126 static const value = unspecified;
127 typedef mpl::bool_<true-or-false> type;
128 };
129
130 The metafunction types and return:
131
132 BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'.
133
134 BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type.
135 If specified it is an MPL lambda expression which is invoked
136 with the inner union found and must return a constant boolean
137 value.
138
139 returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified.
140
141 If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' union
142 exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false.
143
144 If BOOST_TTI_TP_U is specified, then 'value' is true if the 'name' union exists
145 within the enclosing type BOOST_TTI_TP_T and the MPL lambda expression as specified
146 by BOOST_TTI_TP_U, invoked by passing the actual inner union of 'name', returns
147 a 'value' of true; otherwise 'value' is false.
148
149 The action taken with BOOST_TTI_TP_U occurs only when the 'name' union exists
150 within the enclosing type BOOST_TTI_TP_T.
151
152 @endcode
153
154 Example usage:
155
156 @code
157
158 BOOST_TTI_HAS_UNION(MyType) generates the metafunction has_union_MyType in the current scope
159 to look for an inner union called MyType.
160
161 has_union_MyType<EnclosingType>::value is true if MyType is an inner union of EnclosingType, otherwise false.
162
163 has_class_MyType<EnclosingType,ALambdaExpression>::value is true if MyType is an inner union of EnclosingType
164 and invoking ALambdaExpression with the inner union returns a value of true, otherwise false.
165
166 A popular use of the optional MPL lambda expression is to check whether the union found is the same
167 as another type, when the union found is a typedef. In that case our example would be:
168
169 has_union_MyType<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner union
170 of EnclosingType and is the same type as SomeOtherType.
171
172 @endcode
173
174*/
175#define BOOST_TTI_HAS_UNION(name) \
176 BOOST_TTI_TRAIT_HAS_UNION \
177 ( \
178 BOOST_TTI_HAS_UNION_GEN(name), \
179 name \
180 ) \
181/**/
182
183#endif // BOOST_TTI_HAS_UNION_HPP
184

source code of boost/libs/tti/include/boost/tti/has_union.hpp