std::is_rvalue_reference

< cpp‎ | types
Defined in header <type_traits>
template< class T >
struct is_rvalue_reference;
 (since C++11)

std::is_rvalue_reference is an UnaryTypeTrait.

Checks whether T is an rvalue reference type. Provides the member constant value which is equal to true, if T is an rvalue reference type. Otherwise, value is equal to false.

The behavior of a program that adds specializations for std::is_rvalue_reference or std::is_rvalue_reference_v (since C++17) is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
 true if T is an rvalue reference type, false otherwise
(public static member constant)

Member functions

operator bool
 converts the object to bool, returns value
(public member function)
operator()
(C++14)
 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_rvalue_reference : std::false_type {};
template<class T> struct is_rvalue_reference<T&&> : std::true_type {};

Example

#include <type_traits>
 
class A {};
 
static_assert
(
    std::is_rvalue_reference_v<A> == false and
    std::is_rvalue_reference_v<A&> == false and
    std::is_rvalue_reference_v<A&&> != false and
    std::is_rvalue_reference_v<char> == false and
    std::is_rvalue_reference_v<char&> == false and
    std::is_rvalue_reference_v<char&&> != false
);
 
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
    std::cout << "A\t" << std::is_rvalue_reference<A>::value << '\n';
    std::cout << "A&\t" << std::is_rvalue_reference<A&>::value << '\n';
    std::cout << "A&&\t" << std::is_rvalue_reference<A&&>::value << '\n';
    std::cout << "char\t" << std::is_rvalue_reference<char>::value << '\n';
    std::cout << "char&\t" << std::is_rvalue_reference<char&>::value << '\n';
    std::cout << "char&&\t" << std::is_rvalue_reference<char&&>::value << '\n';
}

Output:

A       false
A&      false
A&&     true
char    false
char&   false
char&&  true

See also

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