# 20 General utilities library [utilities]

## 20.9 Function objects [function.objects]

### 20.9.4 Arithmetic operations [arithmetic.operations]

The library provides basic function object classes for all of the arithmetic operators in the language ([expr.mul], [expr.add]).

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

operator() returns x + y.

``` template <class T = void> struct minus { constexpr T operator()(const T& x, const T& y) const; typedef T first_argument_type; typedef T second_argument_type; typedef T result_type; }; ```

operator() returns x - y.

``` template <class T = void> struct multiplies { constexpr T operator()(const T& x, const T& y) const; typedef T first_argument_type; typedef T second_argument_type; typedef T result_type; }; ```

operator() returns x * y.

``` template <class T = void> struct divides { constexpr T operator()(const T& x, const T& y) const; typedef T first_argument_type; typedef T second_argument_type; typedef T result_type; }; ```

operator() returns x / y.

``` template <class T = void> struct modulus { constexpr T operator()(const T& x, const T& y) const; typedef T first_argument_type; typedef T second_argument_type; typedef T result_type; }; ```

operator() returns x % y.

``` template <class T = void> struct negate { constexpr T operator()(const T& x) const; typedef T argument_type; typedef T result_type; }; ```

operator() returns -x.

``` 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)); typedef unspecified is_transparent; }; ```

operator() returns std::forward<T>(t) + std::forward<U>(u).

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

operator() returns std::forward<T>(t) - std::forward<U>(u).

``` template <> struct multiplies<void> { template <class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) * std::forward<U>(u)); typedef unspecified is_transparent; }; ```

operator() returns std::forward<T>(t) * std::forward<U>(u).

``` template <> struct divides<void> { template <class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) / std::forward<U>(u)); typedef unspecified is_transparent; }; ```

operator() returns std::forward<T>(t) / std::forward<U>(u).

``` template <> struct modulus<void> { template <class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) % std::forward<U>(u)); typedef unspecified is_transparent; }; ```

operator() returns std::forward<T>(t) % std::forward<U>(u).

``` template <> struct negate<void> { template <class T> constexpr auto operator()(T&& t) const -> decltype(-std::forward<T>(t)); typedef unspecified is_transparent; }; ```

operator() returns -std::forward<T>(t).