From Pharo Discord:
IIUC when I change the comparison behavior of a class (i.e. reimplement #= and #hash), sets containing those objects start acting oddly e.g. happily storing duplicates of equal objects and failing to find objects they contain. A solution seems to be Set allSubInstances do: #rehash. Is my understanding correct? If so, I find it odd that I've been using and researching Smalltalk for well over a decade and I never remember reading/hearing about this. I wonder if it can be baked into the IDE somehow e.g. via a critic... And stephan responded:
The mailing list posts about that I remember were at the time where the number of object bits used for the hash were increased.
--- Following up on his clue, I found [this old post](https://lists.pharo.org/empathy/thread/LKCE5UXYPXPLVOGNZYW64BWHYJY5NMHQ?hash... "this old post"), which seems to confirm my suspicion. This seems like a serious trap for users to fall into (Iâm having flashbacks to my C++ days lol). So, can/should we somehow handle this in the IDE? Something like a refactoring (that has a confirmation window) that gives you the choice to rehash image collections when redefining these methods? In a 1GB image, \`Set allSubInstances do: #rehash\` is almost instantaneous and \`Dictionary allSubInstances do: #rehash\` takes several seconds.