Defined in header <type_traits> | ||
---|---|---|
template< class T > struct add_lvalue_reference; | (1) | (since C++11) |
template< class T > struct add_rvalue_reference; | (2) | (since C++11) |
Creates a lvalue or rvalue reference type of T
.
1) If
T
is an object or function that isn't cv- or ref- qualified (since C++17), provides a member typedef type
which is T&
. If T
is an rvalue reference to some type U
, then type
is U&
. Otherwise, type
is T
. 2) If
T
is an object or function that isn't cv- or ref- qualified (since C++17), provides a member typedef type
which is T&&
, otherwise type
is T
.Member types
Name | Definition |
---|---|
type | reference to T , or T if not allowed |
Helper types
template< class T > using add_lvalue_reference_t = typename add_lvalue_reference<T>::type; | (since C++14) | |
template< class T > using add_rvalue_reference_t = typename add_rvalue_reference<T>::type; | (since C++14) |
Notes
These type transformations honor reference collapse rules:
std::add_lvalue_reference<T&>::type is T& std::add_lvalue_reference<T&&>::type is T& std::add_rvalue_reference<T&>::type is T& std::add_rvalue_reference<T&&>::type is T&&
Example
#include <iostream> #include <type_traits> int main() { using nonref = int; using lref = typename std::add_lvalue_reference<nonref>::type; using rref = typename std::add_rvalue_reference<nonref>::type; std::cout << std::boolalpha; std::cout << std::is_lvalue_reference<nonref>::value << '\n'; std::cout << std::is_lvalue_reference<lref>::value << '\n'; std::cout << std::is_rvalue_reference<rref>::value << '\n'; }
Output:
false true true
See also
(C++11) | checks if a type is either lvalue reference or rvalue reference (class template) |
(C++11) | removes reference from the given type (class template) |
Please login to continue.