20 General utilities library [utilities]

20.14 Function objects [function.objects]

20.14.4 Class template reference_wrapper [refwrap]

namespace std {
  template <class T> class reference_wrapper {
  public :
    // types
    using type = T;

    // construct/copy/destroy
    reference_wrapper(T&) noexcept;
    reference_wrapper(T&&) = delete;     // do not bind to temporary objects
    reference_wrapper(const reference_wrapper& x) noexcept;

    // assignment
    reference_wrapper& operator=(const reference_wrapper& x) noexcept;

    // access
    operator T& () const noexcept;
    T& get() const noexcept;

    // invocation
    template <class... ArgTypes>
    result_of_t<T&(ArgTypes&&...)>
    operator() (ArgTypes&&...) const;
  };
}
1

reference_wrapper<T> is a CopyConstructible and CopyAssignable wrapper around a reference to an object or function of type T.

2

reference_wrapper<T> shall be a trivially copyable type ([basic.types]).

20.14.4.1 reference_wrapper construct/copy/destroy [refwrap.const]

reference_wrapper(T& t) noexcept;

1

Effects: Constructs a reference_wrapper object that stores a reference to t.

reference_wrapper(const reference_wrapper& x) noexcept;

2

Effects: Constructs a reference_wrapper object that stores a reference to x.get().

20.14.4.2 reference_wrapper assignment [refwrap.assign]

reference_wrapper& operator=(const reference_wrapper& x) noexcept;

1

Postconditions: *this stores a reference to x.get().

20.14.4.3 reference_wrapper access [refwrap.access]

operator T& () const noexcept;

1

Returns: The stored reference.

T& get() const noexcept;

2

Returns: The stored reference.

20.14.4.4 reference_wrapper invocation [refwrap.invoke]

template <class... ArgTypes> result_of_t<T&(ArgTypes&&... )> operator()(ArgTypes&&... args) const;

1

Returns: INVOKE(get(), std::forward<ArgTypes>(args)...). ([func.require])

20.14.4.5 reference_wrapper helper functions [refwrap.helpers]

template <class T> reference_wrapper<T> ref(T& t) noexcept;

1

Returns: reference_wrapper<T>(t).

template <class T> reference_wrapper<T> ref(reference_wrapper<T> t) noexcept;

2

Returns: ref(t.get()).

template <class T> reference_wrapper<const T> cref(const T& t) noexcept;

3

Returns: reference_wrapper <const T>(t).

template <class T> reference_wrapper<const T> cref(reference_wrapper<T> t) noexcept;

4

Returns: cref(t.get()).