reduceOptional abstract method
Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any.
Example
final max = GenericStream.of([1, 2, 3, 4, 5])
.reduceOptional((a, b) => a > b ? a : b);
Implementation
Optional<T> reduceOptional(T Function(T, T) accumulator);