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

NAME
       std::is_rvalue_reference	- std::is_rvalue_reference

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

	  std::is_rvalue_reference is a	UnaryTypeTrait.

	  Checks  whether  T  is an rvalue reference type. Provides the	member
       constant	value
	  which	is equal to true, if T is an rvalue reference type. Otherwise,
       value is	equal
	  to false.

	  If the program adds specializations for std::is_rvalue_reference or
	  std::is_rvalue_reference_v, the behavior is undefined.

Template parameters
	  T - a	type to	check

	  Helper variable template

	  template< class T >
	  inline      constexpr	      bool	 is_rvalue_reference_v	     =
       (since C++17)
	  is_rvalue_reference<T>::value;

       Inherited from std::integral_constant

Member constants
	  value	   true	if T is	an rvalue reference 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
	  template<class T> struct is_rvalue_reference : std::false_type {};
	  template<class  T>  struct is_rvalue_reference<T&&> :	std::true_type
       {};

Example
       // Run this code

	#include <type_traits>
	#include <iostream>

	class A	{};

	static_assert
	(
	    std::is_rvalue_reference_v<A> == false and
	    std::is_rvalue_reference_v<A&> == false and
	    std::is_rvalue_reference_v<A&&> != false and
	    std::is_rvalue_reference_v<char> ==	false and
	    std::is_rvalue_reference_v<char&> == false and
	    std::is_rvalue_reference_v<char&&> != false
	);

	template <typename T>
	void test(T&& x)
	{
	    static_assert(std::is_same_v<T&&, decltype(x)>);
	    std::cout << "T\t" << std::is_rvalue_reference<T>::value <<	'\n';
	    std::cout << "T&&\t"  <<  std::is_rvalue_reference<T&&>::value  <<
       '\n';
	    std::cout	<<   "decltype(x)\t"  <<  std::is_rvalue_reference<de-
       cltype(x)>::value << '\n';
	}

	int main()
	{
	    std::cout << std::boolalpha;
	    std::cout << "A\t" << std::is_rvalue_reference<A>::value <<	'\n';
	    std::cout  <<  "A&\t"  <<  std::is_rvalue_reference<A&>::value  <<
       '\n';
	    std::cout  <<  "A&&\t"  << std::is_rvalue_reference<A&&>::value <<
       '\n';
	    std::cout << "char\t" << std::is_rvalue_reference<char>::value  <<
       '\n';
	    std::cout  <<  "char&\t" <<	std::is_rvalue_reference<char&>::value
       << '\n';
	    std::cout << "char&&\t" << std::is_rvalue_reference<char&&>::value
       << '\n';

	    std::cout << "\ntest(42)\n";
	    test(42);

	    std::cout << "\ntest(x)\n";
	    int	x = 42;
	    test(x);
	}

Output:
	A	false
	A&	false
	A&&	true
	char	false
	char&	false
	char&&	true

	test(42)
	T	false
	T&&	true
	decltype(x)	true

	test(x)
	T	false
	T&&	false
	decltype(x)	false

See also
	  is_lvalue_reference checks if	a type is an lvalue reference
	  (C++11)	      (class template)
	  is_reference	      checks if	a type is either an  lvalue  reference
       or rvalue
	  (C++11)	      reference
			      (class template)

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

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