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.
T is an object type or a function type that has no cv- or ref- qualifier (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.T is an object type or a function type that has no cv- or ref- qualifier (since C++17), provides a member typedef type which is T&&, otherwise type is T.| Name | Definition |
|---|---|
type | reference to T, or T if not allowed |
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) |
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&&
#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
|
(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) |
|
(C++20) | combines std::remove_cv and std::remove_reference (class template) |
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