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)