std::unwrap_reference, std::unwrap_ref_decay

< cpp‎ | utility‎ | functional
 
 
 
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unwrap_referenceunwrap_ref_decay
(C++20)(C++20)
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(until C++17)(until C++17)(until C++17)(until C++17)
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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
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.

Example

See also

CopyConstructible and CopyAssignable reference wrapper
(class template)
creates a pair object of type, defined by the argument types
(function template)
creates a tuple object of the type defined by the argument types
(function template)