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template <class T>
struct is_union : public true_type-or-false_type {};
Inherits: If T is a (possibly cv-qualified) union type then inherits from true_type, otherwise inherits from false_type. Currently requires some kind of compiler support, otherwise unions are identified as classes.
C++ Standard Reference: 3.9.2 and 9.5.
Compiler Compatibility: Without (some as yet unspecified) help from the compiler, we cannot distinguish between union and class types using only standard C++, as a result this type will never inherit from true_type, unless the user explicitly specializes the template for their user-defined union types, or unless the compiler supplies some unspecified intrinsic that implements this functionality. Currently (May 2005) only Visual C++ 8 has the necessary compiler intrinsics to make this trait "just work" without user intervention.
Header: #include
<boost/type_traits/is_union.hpp>
or #include <boost/type_traits.hpp>
Examples:
is_union<void>inherits fromtrue_type.
is_union<const void>::typeis the typetrue_type.
is_union<void>::valueis an integral constant expression that evaluates to true.
is_union<void*>::valueis an integral constant expression that evaluates to false.
is_union<T>::value_typeis the typebool.