Function result cacheing

This has been discussed before in the context of misunderstanding the
meaning of 'iscachable', but I now have a use for cached function results,
and have seen at least one other posting with a similar need.

The reason I need it is that I have a few functions that do recursive
inheritance lookups going up a converging inheritance tree. Typically this
function will be called on several hundred objects in a single select
statement. Because of inheritance, it ends up with several thousand
function calls, each of which is non-trivial.

A solution that would be useful for me would be:

If a function is marked 'invariant' (or something similar), then

- cache the most recently used 20 calls (config item) iff the args were
less than 1K in total storage (ie. don't cache large text blocks),

- calculate a very simple checksum on the args

- when a function is to be evaluated, calc the checksum and if a match is
found, compare the args, and if they all match, return the result.

I would anticipate deleting the cache when the current command exits,
and/or certainly when a TX ends.

Obviously this is not a 7.3 item, but would people support such
functionality going into a future version?

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