23 General utilities library [utilities]

23.14 Function objects [function.objects]

23.14.6 Arithmetic operations [arithmetic.operations]

23.14.6.1 Class template plus [arithmetic.operations.plus]

template <class T = void> struct plus { constexpr T operator()(const T& x, const T& y) const; };

constexpr T operator()(const T& x, const T& y) const;

Returns: x + y.

template <> struct plus<void> { template <class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) + std::forward<U>(u)); using is_transparent = unspecified; };

template <class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) + std::forward<U>(u));

Returns: std​::​forward<T>(t) + std​::​forward<U>(u).