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