22 General utilities library [utilities]

22.10 Function objects [function.objects]

22.10.6 Class template reference_wrapper [refwrap] General [refwrap.general]

namespace std { template<class T> class reference_wrapper { public: // types using type = T; // [refwrap.const], constructors template<class U> constexpr reference_wrapper(U&&) noexcept(see below); constexpr reference_wrapper(const reference_wrapper& x) noexcept; // [refwrap.assign], assignment constexpr reference_wrapper& operator=(const reference_wrapper& x) noexcept; // [refwrap.access], access constexpr operator T& () const noexcept; constexpr T& get() const noexcept; // [refwrap.invoke], invocation template<class... ArgTypes> constexpr invoke_result_t<T&, ArgTypes...> operator()(ArgTypes&&...) const noexcept(is_nothrow_invocable_v<T&, ArgTypes...>); // [refwrap.comparisons], comparisons friend constexpr bool operator==(reference_wrapper, reference_wrapper); friend constexpr bool operator==(reference_wrapper, const T&); friend constexpr bool operator==(reference_wrapper, reference_wrapper<const T>); friend constexpr synth-three-way-result<T> operator<=>(reference_wrapper, reference_wrapper); friend constexpr synth-three-way-result<T> operator<=>(reference_wrapper, const T&); friend constexpr synth-three-way-result<T> operator<=>(reference_wrapper, reference_wrapper<const T>); }; template<class T> reference_wrapper(T&) -> reference_wrapper<T>; }
reference_wrapper<T> is a Cpp17CopyConstructible and Cpp17CopyAssignable wrapper around a reference to an object or function of type T.
reference_wrapper<T> is a trivially copyable type ([basic.types.general]).
The template parameter T of reference_wrapper may be an incomplete type.
[Note 1: 
Using the comparison operators described in subclause [refwrap.comparisons] with T being an incomplete type can lead to an ill-formed program with no diagnostic required ([temp.point], [temp.constr.atomic]).
— end note]