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Showing content from https://en.cppreference.com/w/cpp/language/../error/../language/../types/is_reference.html below:

std::is_reference - cppreference.com

template< class T > struct is_reference;

(since C++11)

std::is_reference is a UnaryTypeTrait.

If T is a reference type (lvalue reference or rvalue reference), provides the member constant value equal true. For any other type, value is false.

If the program adds specializations for std::is_reference or std::is_reference_v, the behavior is undefined.

[edit] Template parameters [edit] Helper variable template

template< class T > constexpr bool is_reference_v = is_reference<T>::value;

(since C++17) Inherited from std::integral_constant Member constants true if T is a 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 [edit] Possible implementation [edit] Example

#include <iostream>
#include <type_traits>
 
class A {};
 
int main()
{
#   define REF(x) << #x " ?: " << x << '\n'
    std::cout << std::boolalpha
    REF(std::is_reference_v<A>)
    REF(std::is_reference_v<A&>)
    REF(std::is_reference_v<A&&>)
    REF(std::is_reference_v<long>)
    REF(std::is_reference_v<long&>)
    REF(std::is_reference_v<long&&>)
    REF(std::is_reference_v<double*>)
    REF(std::is_reference_v<double*&>)
    REF(std::is_reference_v<double*&&>);
#   undef REF
}

Output:

std::is_reference_v<A> ?: false
std::is_reference_v<A&> ?: true
std::is_reference_v<A&&> ?: true
std::is_reference_v<long> ?: false
std::is_reference_v<long&> ?: true
std::is_reference_v<long&&> ?: true
std::is_reference_v<double*> ?: false
std::is_reference_v<double*&> ?: true
std::is_reference_v<double*&&> ?: true

[edit] See also

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