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 constant 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)