`ic_stable_structures`: How do we iterate in reverse order?

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It seems ic_stable_structures BTreeMap and Vec do not implement the DoubleEndedIterator trait for their Iterators.

How do we .iter().rev() on these structures?
(Iterate by shared reference in reverse order)

@ielashi

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Hi @Samer, a DoubleEndedIterator has already been implemented for Vec in this PR but it hasn’t been released yet. I believe @hpeebles is planning on writing a DoubleEndedIterator for BTreeMap as well, and without that, iterating in reverse order in BTreeMap is not yet possible unfortunately.

I created an issue to track this.

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I would love to implement it for BTreeMap if I get time, but realistically its unlikely I’ll do it any time soon since it isn’t a high priority for me compared to some of the OpenChat stuff we have lined up.

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The workaround is obvious for now.

We convert (parts of) the stable structure into a heap structure and reverse iterate on that. This works for small data sets for now

Looking forward to the impl!

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