Use case

The default implementation of .elementAt is O(n) as it goes through the iterable.
CachingIterable could implement it in amortised O(1) as it is, without any extra complexity, given that it caches results in a list.

Proposal

Possible implementation:

  @override
  E elementAt(int index) {
    while (_results.length <= index) {
      if (!_fillNext()) {
        throw RangeError.index(index, this, 'index', 'Index out of range');
      }
    }
    return _results[index];
  }