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

NAME
       std::is_class - std::is_class

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

	  Checks whether T is a	non-union class	type. Provides the member con-
       stant value which
	  is  equal  to	true, if T is a	class type (but	not union). Otherwise,
       value is	equal to
	  false.

	  The behavior of a program that adds specializations for is_class
	  or is_class_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_class_v = is_class<T>::value;

       Inherited from std::integral_constant

Member constants
	  value	   true	if T is	a non-union 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::integral_constant<bool,	  !std::is_union<T>::value>   test(int
       T::*);

	  template <class>
	  std::false_type test(...);
	  }

	  template <class T>
	  struct is_class : decltype(detail::test<T>(nullptr))
	  {};

Example
       // Run this code

	#include <iostream>
	#include <type_traits>

	struct A {};

	class B	{};

	enum class E {};

	union U	{ class	UC {}; };
	static_assert(not std::is_class_v<U>);
	static_assert(std::is_class_v<U::UC>);

	int main()
	{
	    std::cout << std::boolalpha;
	    std::cout << std::is_class<A>::value << ": A\n";
	    std::cout << std::is_class_v<B> << ": B \n";
	    std::cout << std::is_class_v<B*> <<	": B* \n";
	    std::cout << std::is_class_v<B&> <<	": B& \n";
	    std::cout << std::is_class_v<const B> << ":	const B	\n";
	    std::cout << std::is_class<E>::value << ": E\n";
	    std::cout << std::is_class_v<int> << ": int\n";
	    std::cout << std::is_class_v<struct	S>  <<	":  struct  S  (incom-
       plete)\n";
	    std::cout  <<  std::is_class_v<class  C>  <<  ":  class  C (incom-
       plete)\n";
	}

Output:
	true: A
	true: B
	false: B*
	false: B&
	true: const B
	false: E
	false: int
	true: struct S (incomplete)
	true: class C (incomplete)

See also
	  is_union checks if a type is an union	type
	  (C++11)  (class template)

http://cppreference.com		  2022.07.31		      std::is_class(3)

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