std::is_rvalue_reference - cppreference.com (original) (raw)

| | | | | -------------------------------------------------- | | ------------- | | template< class T > struct is_rvalue_reference; | | (since C++11) |

std::is_rvalue_reference is a 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.

If the program adds specializations for std::is_rvalue_reference or std::is_rvalue_reference_v, the behavior is undefined.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Possible implementation
  • 3.5 Example
  • 3.6 See also

[edit] Template parameters

[edit] Helper variable template

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

Inherited from std::integral_constant

Member constants

| | true if T is an rvalue 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 #include   class A {};   static_assert ( std::is_rvalue_reference_v == false and std::is_rvalue_reference_v<A&> == false and std::is_rvalue_reference_v<A&&> != false and std::is_rvalue_reference_v == false and std::is_rvalue_reference_v<char&> == false and std::is_rvalue_reference_v<char&&> != false );   template void test(T&& x) { static_assert(std::is_same_v<T&&, decltype(x)>); std::cout << "T\t" << std::is_rvalue_reference::value << '\n'; std::cout << "T&&\t" << std::is_rvalue_reference<T&&>::value << '\n'; std::cout << "decltype(x)\t" << std::is_rvalue_reference<decltype(x)>::value << '\n'; }   int main() { std::cout << std::boolalpha; std::cout << "A\t" << std::is_rvalue_reference::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::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 << "\ntest(42)\n"; test(42);   std::cout << "\ntest(x)\n"; int x = 42; test(x); }

Output:

A false A& false A&& true char false char& false char&& true   test(42) T false T&& true decltype(x) true   test(x) T false T&& false decltype(x) false

[edit] See also