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std::unwrap_reference, std::unwrap_ref_decay

Defined in header `<functional>`
template< class T > struct unwrap_reference;	(1)	(since C++20)
template< class T > struct unwrap_ref_decay : std::unwrap_reference<std::decay_t<T>> {};	(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>.

Member types

Name Definition

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.

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_ref_decay_t = typename unwrap_ref_decay<T>::type;

(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&; };

Notes

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

reference_wrapper (C++11)	CopyConstructible and CopyAssignable reference wrapper (class template)
make_pair	creates a `pair` object of type, defined by the argument types (function template)
make_tuple	creates a `tuple` object of the type defined by the argument types (function template)