If you want to implement this on your own you need to
- walk the "delta" structure bottom-up and
- delete the corresponding entries in the "augmented" structure by rules
- Rule1: delete simple scalars
- Rule2: delete only empty containers (hashes&arrays)
For Rule2 it's crucial that you walked bottom up. If there are childrens left after deleting all delta-childrens you can't be allowed to delete a container.
The walking can be done with a recursive function which does the deleting after recursing just before returning.
Hence all childrens at the "bottom" have already been processed.
HTH! :)
edit
FWIW: for augmenting you can use the same walker for the delta, just top-down.
I.e. you "augment" new elements just before recursing.
(actually thanks to auto-vivification this can be done more easily by only adding the leaves of the tree, but not much wrong with a clean symmetric algorithm? :)
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