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

NAME
     std::is_polymorphic - std::is_polymorphic

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

	std::is_polymorphic is a UnaryTypeTrait.

	If T is a polymorphic class (that is, a non-union class that declares or
     inherits at
	least one 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_polymorphic or
	std::is_polymorphic_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_polymorphic_v = is_polymorphic<T>::value;

     Inherited from std::integral_constant

Member constants
	value	 true if T is a polymorphic 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>

Possible implementation
	namespace detail
	{
	    template<class T>
	    std::true_type detect_is_polymorphic(
		decltype(dynamic_cast<const	    volatile	     void*>(sta-
     tic_cast<T*>(nullptr)))
	    );
	    template<class T>
	    std::false_type detect_is_polymorphic(...);
	} // namespace detail

	template<class T>
	struct	    is_polymorphic     :     decltype(detail::detect_is_polymor-
     phic<T>(nullptr)) {};

Example
     // Run this code

      #include <type_traits>

      struct A { int m; };
      static_assert(!std::is_polymorphic_v<A>);

      struct B { virtual void foo(); };
      static_assert(std::is_polymorphic_v<B>);

      struct C : B {};
      static_assert(std::is_polymorphic_v<C>);

      struct D { virtual ~D() = default; };
      static_assert(std::is_polymorphic_v<D>);

      // Uses inheritance, but not the virtual keyword:
      struct E : A {};
      static_assert(!std::is_polymorphic_v<E>);

      struct F : virtual A {};
      static_assert(!std::is_polymorphic_v<F>);

      struct AX : A {};
      struct AY : A {};
      struct XY : virtual AX, virtual AY {};
      static_assert(!std::is_polymorphic_v<XY>);

      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_abstract	       checks if a type is an abstract class type
	(C++11) 	       (class template)
	has_virtual_destructor checks if a type has a virtual destructor
	(C++11) 	       (class template)

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