std::is_lvalue_reference - cppreference.com

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template< class T > struct is_lvalue_reference;		(since C++11)

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

Helper variable template

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

Inherited from std::integral_constant

Member constants

true if T is an lvalue reference type, false otherwise
(public static member constant)

Member functions

	converts the object to `bool`, returns `value` (public member function)
	returns `value` (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

#include <type_traits>

class A {};
static_assert(std::is_lvalue_reference_v<A> == false);
static_assert(std::is_lvalue_reference_v<A&> == true);
static_assert(std::is_lvalue_reference_v<A&&> == false);

static_assert(std::is_lvalue_reference_v<int> == false);
static_assert(std::is_lvalue_reference_v<int&> == true);
static_assert(std::is_lvalue_reference_v<int&&> == false);

int main() {}