Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
template <class T>
struct is_class : public true_type-or-false_type {};
Inherits: If T is a (possibly cv-qualified) class type (and not a union type) then inherits from true_type, otherwise inherits from false_type.
C++ Standard Reference: 3.9.2 and 9.2.
Header: #include
<boost/type_traits/is_class.hpp>
or #include <boost/type_traits.hpp>
Compiler Compatibility: Without (some as
yet unspecified) help from the compiler, we cannot distinguish between union
and class types, as a result this type will erroneously inherit from true_type for
union types. See also is_union.
Currently (May 2011) compilers more recent than Visual C++ 8, GCC-4.3, Greenhills
6.0, Intel-11.0, and Codegear have the necessary compiler intrinsics
to ensure that this trait "just works". You may also test to see
if the necessary intrinsics
are available by checking to see if the macro BOOST_IS_CLASS
is defined.
Examples:
Given:
class MyClass;then:
is_class<MyClass>inherits fromtrue_type.
is_class<MyClass const>::typeis the typetrue_type.
is_class<MyClass>::valueis an integral constant expression that evaluates to true.
is_class<MyClass&>::valueis an integral constant expression that evaluates to false.
is_class<MyClass*>::valueis an integral constant expression that evaluates to false.
is_class<T>::value_typeis the typebool.