27 Algorithms library [algorithms]

27.10 Generalized numeric operations [numeric.ops]

27.10.3 Accumulate [accumulate]

template<class InputIterator, class T> constexpr T accumulate(InputIterator first, InputIterator last, T init); template<class InputIterator, class T, class BinaryOperation> constexpr T accumulate(InputIterator first, InputIterator last, T init, BinaryOperation binary_op);
Preconditions: T meets the Cpp17CopyConstructible (Table 32) and Cpp17CopyAssignable (Table 34) requirements.
In the range [first, last], binary_op neither modifies elements nor invalidates iterators or subranges.215
Effects: Computes its result by initializing the accumulator acc with the initial value init and then modifies it with acc = std​::​move(acc) + *i or acc = binary_op(std​::​move(acc), *i) for every iterator i in the range [first, last) in order.216
The use of fully closed ranges is intentional.
accumulate is similar to the APL reduction operator and Common Lisp reduce function, but it avoids the difficulty of defining the result of reduction on an empty sequence by always requiring an initial value.