std::unwrap_reference, std::unwrap_ref_decay

< cpp‎ | utility‎ | functional

Defined in header `<type_traits>`
Defined in header `<functional>`
template< class T > struct unwrap_reference;	(1)	(since C++20)
template< class T > struct unwrap_ref_decay;	(2)	(since C++20)

1) If T is std::reference_wrapper<U> for some type U, provides a member typedef type that names U&; otherwise, provides a member typedef type that names T.

2) If T is std::reference_wrapper<U> for some type U, ignoring cv-qualification and referenceness, provides a member typedef type that names U&; otherwise, provides a member typedef type that names std::decay_t<T>.

The behavior of a program that adds specializations for any of the templates described on this page is undefined.

Member types

Name Definition

type

1) U& if T is std::reference_wrapper<U>; T otherwise

2) U& if std::decay_t<T> is std::reference_wrapper<U>; std::decay_t<T> otherwise

Helper types

template<class T> using unwrap_reference_t = typename unwrap_reference<T>::type;	(1)	(since C++20)
template<class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type;	(2)	(since C++20)

Possible implementation

template <class T>
struct unwrap_reference { using type = T; };
template <class U>
struct unwrap_reference<std::reference_wrapper<U>> { using type = U&; };
 
template< class T >
struct unwrap_ref_decay : std::unwrap_reference<std::decay_t<T>> {};

Notes

std::unwrap_ref_decay performs the same transformation as used by std::make_pair and std::make_tuple.

Example

This section is incomplete
Reason: no example