Re: WIP: extensible enums

Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> writes:
> Hmm, it's harder than I thought. The crash is because each time it
> finds a label it hasn't seen before it adds it to the array of cached
> values without checking the array bounds. That array is only as big as
> the number of elements in the enum the first time it was called.

[ scratches head... ] And where does it get that number of elements
from, if not by doing the same work that would allow it to fill the
array completely? Something seems ill-designed here.

> Allowing the array to grow would prevent crashes, but not protect
> again returning incorrect answers.

Well, one of the questions here is exactly how wrong the answers can
be. Offhand, it seems to me that comparisons of two existing entries
can never be falsified by adding a new entry, so I'm not seeing that
there could be any real problem. If we allowed rearrangement of the
sort order of existing entries, it'd be problematic.

> Perhaps it should just read and cache all the values the first time it
> is called. Then if it ever fails to find a value in the array, it
> knows that the enum must have grown, and it can rebuild the whole
> array.

This is kept in typcache, right? ISTM the right thing to do is arrange
to invalidate the cached array when a cache flush event occurs, and
rebuild the whole array on next use. Then you just throw an error if
you're passed a value that isn't there.

regards, tom lane