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

NAME
     std::is_integral - std::is_integral

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

	std::is_integral is a UnaryTypeTrait.

	Checks whether T is an integral type. Provides the member constant value
     which is
	equal to true, if T is the type bool, char
	, char8_t
	(since C++20), char16_t, char32_t, wchar_t, short, int, long, long long,
     or any
	implementation-defined extended integer types, including any signed, un-
     signed, and
	cv-qualified variants. Otherwise, value is equal to false.

	If  the program adds specializations for std::is_integral or std::is_in-
     tegral_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_integral_v = is_integral<T>::value;

     Inherited from std::integral_constant

Member constants
	value	 true if T is an integral 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
	// Note: this implementation uses C++20 facilities
	template<class T>
	struct is_integral : std::bool_constant<
	    requires  (T  t, T* p, void (*f)(T)) // T* parameter excludes refer-
     ence types
	    {
		reinterpret_cast<T>(t); // Exclude class types
		f(0); // Exclude enumeration types
		p + t; // Exclude everything not yet excluded but integral types
	    }> {};

Example
     // Run this code

      #include <type_traits>

      static_assert
      (
	  std::is_integral_v<float> == false &&
	  std::is_integral_v<int*> == false &&
	  std::is_integral_v<int> == true &&
	  std::is_integral_v<const int> == true &&
	  std::is_integral_v<bool> == true &&
	  std::is_integral_v<char> == true
      );

      class A {};
      static_assert(std::is_integral_v<A> == false);

      struct B { int x:4; };
      static_assert(std::is_integral_v<B> == false);
      using BF = decltype(B::x); // bit-field's type
      static_assert(std::is_integral_v<BF> == true);

      enum E : int {};
      static_assert(std::is_integral_v<E> == false);

      template <class T>
      constexpr T same(T i)
      {
	  static_assert(std::is_integral<T>::value, "Integral required.");
	  return i;
      }
      static_assert(same('"') == 042);

      int main() {}

See also
	integral	  specifies that a type is an integral type
	(C++20) 	  (concept)
	is_integer	  identifies integer types
	[static]	  (public static member  constant  of  std::numeric_lim-
     its<T>)
	is_floating_point checks if a type is a floating-point type
	(C++11) 	  (class template)
	is_arithmetic	  checks if a type is an arithmetic type
	(C++11) 	  (class template)
	is_enum 	  checks if a type is an enumeration type
	(C++11) 	  (class template)

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