*<Null safety>*
T reduceIndexed (T combine(int index, T previous, T element))
T reduceIndexed(T Function(int index, T previous, T element) combine) { var iterator = this.iterator; if (!iterator.moveNext()) { throw StateError('no elements'); } var index = 1; var result = iterator.current; while (iterator.moveNext()) { result = combine(index++, result, iterator.current); } return result; }