> Using metatables, I'd imagine this would be easy to implement. The
__newindex method is provided to catch new entries to the table, which is
> where you count new entries. I'd go a step further and memoize a
function that returned these counts, and use the table itself as a key in the
> memoization.
I think you'd run into the problem that there isn't any metamethod called
when a table entry is set to nil (aka deleted)?