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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;

	std::is_class is a UnaryTypeTrait.

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

	If    the    program   adds   specializations	for   std::is_class   or
     std::is_class_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_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 (incomplete)\n";
	  std::cout << std::is_class_v<class C> << ": class C (incomplete)\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 a union type
	(C++11)  (class template)

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