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std::add_lvalue_reference, std::add_rvalue_reference

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add_lvalue_referenceadd_rvalue_reference
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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, 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, provides a member typedef type which is T&&, otherwise type is T.

Contents

[edit] Member types

Name Definition
type reference to T, or T if not allowed

[edit] 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)

[edit] 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&&

[edit] 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

[edit] See also

checks if a type is either lvalue reference or rvalue reference
(class template) [edit]
removes reference from the given type
(class template) [edit]