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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;

	  If  T	 is  a	polymorphic class (that	is, a non-union	class that de-
       clares 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 a non-union	class type, T shall be a complete type;	other-
       wise, the behavior
	  is undefined.

	  The behavior of a program that adds specializations for  is_polymor-
       phic
	  or is_polymorphic_v
	  (since C++17)	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 <iostream>
	#include <type_traits>

	struct A {
	    int	m;
	};

	struct B {
	    virtual void foo();
	};

	struct C : B {};

	struct D {
	    virtual ~D() = default;
	};

	int main()
	{
	    std::cout << std::boolalpha
		      << std::is_polymorphic<A>::value << ' '
		      << std::is_polymorphic<B>::value << ' '
		      << std::is_polymorphic<C>::value << ' '
		      << std::is_polymorphic<D>::value << '\n';
	}

Output:
	false true true	true

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		  2022.07.31		std::is_polymorphic(3)

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