std::add_lvalue_reference, std::add_rvalue_reference

 

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is_lvalue_reference (C++11)
is_rvalue_reference (C++11)
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is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)
is_assignable is_trivially_assignable is_nothrow_assignable (C++11) (C++11) (C++11)
is_copy_assignable is_trivially_copy_assignable is_nothrow_copy_assignable (C++11) (C++11) (C++11)
is_move_assignable is_trivially_move_assignable is_nothrow_move_assignable (C++11) (C++11) (C++11)
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Type trait constants
integral_constant (C++11)

 

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)

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.

Member types

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

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

run this code

#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

is_reference (C++11)	checks if a type is either lvalue reference or rvalue reference (class template)
remove_reference (C++11)	removes reference from the given type (class template)