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

NAME
     std::is_lvalue_reference - std::is_lvalue_reference

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

	std::is_lvalue_reference is a UnaryTypeTrait.

	Checks	whether  T is an lvalue reference type. Provides the member con-
     stant value
	which is equal to true, if T is an  lvalue  reference  type.  Otherwise,
     value is equal
	to false.

	If the program adds specializations for std::is_lvalue_reference or
	std::is_lvalue_reference_v, the behavior is undefined.

Template parameters
	T - a type to check

	Helper variable template

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

     Inherited from std::integral_constant

Member constants
	value	 true if T is an lvalue 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_lvalue_reference	 : std::false_type {};
	template<class T> struct is_lvalue_reference<T&> : std::true_type {};

Example
     // Run this code

      #include <iostream>
      #include <type_traits>

      class A {};

      int main()
      {
	  std::cout << std::boolalpha;
	  std::cout << std::is_lvalue_reference<A>::value << '\n';
	  std::cout << std::is_lvalue_reference<A&>::value << '\n';
	  std::cout << std::is_lvalue_reference<A&&>::value << '\n';
	  std::cout << std::is_lvalue_reference<int>::value << '\n';
	  std::cout << std::is_lvalue_reference<int&>::value << '\n';
	  std::cout << std::is_lvalue_reference<int&&>::value << '\n';
      }

Output:
      false
      true
      false
      false
      true
      false

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

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