20 General utilities library [utilities]

20.14 Function objects [function.objects]

20.14.5 Class template reference_­wrapper [refwrap] Helper functions [refwrap.helpers]

The template parameter T of the following ref and cref function templates may be an incomplete type.
template<class T> reference_wrapper<T> ref(T& t) noexcept;
Returns: reference_­wrapper<T>(t).
template<class T> reference_wrapper<T> ref(reference_wrapper<T> t) noexcept;
Returns: ref(t.get()).
template<class T> reference_wrapper<const T> cref(const T& t) noexcept;
Returns: reference_­wrapper <const T>(t).
template<class T> reference_wrapper<const T> cref(reference_wrapper<T> t) noexcept;
Returns: cref(t.get()).