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std::is_abstract(3)	       C++ Standard Libary	     std::is_abstract(3)

NAME
     std::is_abstract - std::is_abstract

Synopsis
	Defined in header <type_traits>
	template< class T >		 (since C++11)
	struct is_abstract;

	std::is_abstract is a UnaryTypeTrait.

	If  T  is an abstract class (that is, a non-union class that declares or
     inherits at
	least one pure virtual function), provides  the  member  constant  value
     equal to true.
	For any other type, value is false.

	If T is an incomplete non-union class type, the behavior is undefined.

	If  the program adds specializations for std::is_abstract or std::is_ab-
     stract_v, the
	behavior is undefined.

Template parameters
	T - a type to check

	Helper variable template

	template<  class  T  >						  (since
     C++17)
	inline constexpr bool is_abstract_v = is_abstract<T>::value;

     Inherited from std::integral_constant

Member constants
	value	 true if T is an abstract class type, false otherwise
	[static] (public static member constant)

Member functions
	operator bool converts the object to bool, returns value
		      (public member function)
	operator()    returns value
	(C++14)       (public member function)

Member types
	Type	   Definition
	value_type bool
	type	   std::integral_constant<bool, value>

Example
     // Run this code

      #include <iostream>
      #include <type_traits>

      struct A { int m; };
      static_assert(std::is_abstract_v<A> == false);

      struct B { virtual void foo(); };
      static_assert(std::is_abstract_v<B> == false);

      struct C { virtual void foo() = 0; };
      static_assert(std::is_abstract_v<C> == true);

      struct D : C {};
      static_assert(std::is_abstract_v<D> == true);

      int main() {}

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	Behavior as published		Correct behavior
	LWG 2015 C++11	    the behavior was undefined if the base  characteris-
     tic is
			    T  is  an  incomplete  union type std::false_type in
     this case

See also
	is_class       checks if a type is a non-union class type
	(C++11)        (class template)
	is_polymorphic checks if a type is a polymorphic class type
	(C++11)        (class template)

http://cppreference.com 	   2024.06.10		     std::is_abstract(3)
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