# std::is_rvalue_reference

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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

Run this code

    #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

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

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