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### is_abstract

    template <class T>
    struct is_abstract : public true_type-or-false_type {};

Inherits: If T is a (possibly cv-qualified) abstract type then inherits from true_type, otherwise inherits from false_type.

C++ Standard Reference: 10.3.

Header: `#include <boost/type_traits/is_abstract.hpp>` or `#include <boost/type_traits.hpp>`

Compiler Compatibility: The compiler must support DR337 (as of April 2005: GCC 3.4, VC++ 7.1 (and later), Intel C++ 7 (and later), and Comeau 4.3.2). Otherwise behaves the same as is_polymorphic; this is the "safe fallback position" for which polymorphic types are always regarded as potentially abstract. The macro BOOST_NO_IS_ABSTRACT is used to signify that the implementation is buggy, users should check for this in their own code if the "safe fallback" is not suitable for their particular use-case.

Examples:

> Given: `class abc{ virtual ~abc() = 0; };`

> `is_abstract<abc>` inherits from `true_type`.

> `is_abstract<abc>::type` is the type `true_type`.

> `is_abstract<abc const>::value` is an integral constant expression that evaluates to true.

> `is_abstract<T>::value_type` is the type `bool`.