--- /dev/null
+
+// (C) Copyright Edward Diener 2019
+// Use, modification and distribution are subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt).
+
+#if !defined(BOOST_TTI_HAS_UNION_HPP)
+#define BOOST_TTI_HAS_UNION_HPP
+
+#include <boost/config.hpp>
+#include <boost/preprocessor/cat.hpp>
+#include <boost/tti/gen/has_union_gen.hpp>
+#include <boost/tti/gen/namespace_gen.hpp>
+#include <boost/tti/detail/dunion.hpp>
+#include <boost/tti/detail/ddeftype.hpp>
+
+/*
+
+ The succeeding comments in this file are in doxygen format.
+
+*/
+
+/** \file
+*/
+
+/// A macro which expands to a metafunction which tests whether an inner union with a particular name exists.
+/**
+
+ BOOST_TTI_TRAIT_HAS_UNION is a macro which expands to a metafunction.
+ The metafunction tests whether an inner union with a particular name exists
+ and, optionally, whether an MPL lambda expression invoked with the inner union
+ is true or not. The macro takes the form of BOOST_TTI_TRAIT_HAS_UNION(trait,name) where
+
+ trait = the name of the metafunction <br/>
+ name = the name of the inner union.
+
+ BOOST_TTI_TRAIT_HAS_UNION generates a metafunction called "trait" where 'trait' is the macro parameter.
+
+ @code
+
+ template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U>
+ struct trait
+ {
+ static const value = unspecified;
+ typedef mpl::bool_<true-or-false> type;
+ };
+
+ The metafunction types and return:
+
+ BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'.
+ The enclosing type can be a class, struct, or union.
+
+ BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type.
+ If specified it is an MPL lambda expression which is invoked
+ with the inner union found and must return a constant boolean
+ value.
+
+ returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified.
+
+ If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' union
+ exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false.
+
+ If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' union exists
+ within the enclosing type BOOST_TTI_TP_T and the MPL lambda expression as specified
+ by BOOST_TTI_TP_U, invoked by passing the actual inner union of 'name', returns
+ a 'value' of true; otherwise 'value' is false.
+
+ The action taken with BOOST_TTI_TP_U occurs only when the 'name' union exists
+ within the enclosing type BOOST_TTI_TP_T.
+
+ @endcode
+
+ Example usage:
+
+ @code
+
+ BOOST_TTI_TRAIT_HAS_UNION(LookFor,MyType) generates the metafunction LookFor in the current scope
+ to look for an inner union called MyType.
+
+ LookFor<EnclosingType>::value is true if MyType is an inner union of EnclosingType, otherwise false.
+
+ LookFor<EnclosingType,ALambdaExpression>::value is true if MyType is an inner union of EnclosingType
+ and invoking ALambdaExpression with the inner union returns a value of true, otherwise false.
+
+ A popular use of the optional MPL lambda expression is to check whether the union found is the same
+ as another type, when the union found is a typedef. In that case our example would be:
+
+ LookFor<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner union
+ of EnclosingType and is the same type as SomeOtherType.
+
+ @endcode
+
+*/
+#define BOOST_TTI_TRAIT_HAS_UNION(trait,name) \
+ BOOST_TTI_DETAIL_TRAIT_HAS_UNION(trait,name) \
+ template \
+ < \
+ class BOOST_TTI_TP_T, \
+ class BOOST_TTI_TP_U = BOOST_TTI_NAMESPACE::detail::deftype \
+ > \
+ struct trait \
+ { \
+ typedef typename \
+ BOOST_PP_CAT(trait,_detail_union)<BOOST_TTI_TP_T,BOOST_TTI_TP_U>::type type; \
+ BOOST_STATIC_CONSTANT(bool,value=type::value); \
+ }; \
+/**/
+
+/// A macro which expands to a metafunction which tests whether an inner union with a particular name exists.
+/**
+
+ BOOST_TTI_HAS_UNION is a macro which expands to a metafunction.
+ The metafunction tests whether an inner union with a particular name exists
+ and, optionally, whether an MPL lambda expression invoked with the inner union
+ is true or not. The macro takes the form of BOOST_TTI_HAS_UNION(name) where
+
+ name = the name of the inner union.
+
+ BOOST_TTI_HAS_UNION generates a metafunction called "has_union_'name'" where 'name' is the macro parameter.
+
+ @code
+
+ template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U>
+ struct has_union_'name'
+ {
+ static const value = unspecified;
+ typedef mpl::bool_<true-or-false> type;
+ };
+
+ The metafunction types and return:
+
+ BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'.
+
+ BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type.
+ If specified it is an MPL lambda expression which is invoked
+ with the inner union found and must return a constant boolean
+ value.
+
+ returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified.
+
+ If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' union
+ exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false.
+
+ If BOOST_TTI_TP_U is specified, then 'value' is true if the 'name' union exists
+ within the enclosing type BOOST_TTI_TP_T and the MPL lambda expression as specified
+ by BOOST_TTI_TP_U, invoked by passing the actual inner union of 'name', returns
+ a 'value' of true; otherwise 'value' is false.
+
+ The action taken with BOOST_TTI_TP_U occurs only when the 'name' union exists
+ within the enclosing type BOOST_TTI_TP_T.
+
+ @endcode
+
+ Example usage:
+
+ @code
+
+ BOOST_TTI_HAS_UNION(MyType) generates the metafunction has_union_MyType in the current scope
+ to look for an inner union called MyType.
+
+ has_union_MyType<EnclosingType>::value is true if MyType is an inner union of EnclosingType, otherwise false.
+
+ has_class_MyType<EnclosingType,ALambdaExpression>::value is true if MyType is an inner union of EnclosingType
+ and invoking ALambdaExpression with the inner union returns a value of true, otherwise false.
+
+ A popular use of the optional MPL lambda expression is to check whether the union found is the same
+ as another type, when the union found is a typedef. In that case our example would be:
+
+ has_union_MyType<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner union
+ of EnclosingType and is the same type as SomeOtherType.
+
+ @endcode
+
+*/
+#define BOOST_TTI_HAS_UNION(name) \
+ BOOST_TTI_TRAIT_HAS_UNION \
+ ( \
+ BOOST_TTI_HAS_UNION_GEN(name), \
+ name \
+ ) \
+/**/
+
+#endif // BOOST_TTI_HAS_UNION_HPP
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