Dart: Scalable Application Development

BidirectionalIterator

Sometimes, we need to iterate over a collection of elements in both directions. To help in such cases, Dart provides BidirectionalIterator. In the following code, BiListIterator is the implementation of BidirectionalIterator:

class BiListIterator<E> implements BidirectionalIterator<E> {
  final Iterable<E> _iterable;
  final int _length;
  int _index;
  E _current;

The constructor has an extra optional back parameter that defines the direction of the iteration:

  BiListIterator(Iterable<E> iterable, {bool back:false}) :
    _iterable = iterable, _length = iterable.length,
    _index = back ? iterable.length - 1 : 0;

  E get current => _current;

The following code shows the moveNext method of the Iterator to move forward. This and the next method ...