Daniel Slomovits wrote:

A user working on their own application and modifying a #=/#hash implementation there has a very straightforward way to resolve the problem���"reboot" their own application, tearing down and rebuilding any structures it uses.

For a developer in the common usage, as distinct from a user, I suspect you may be right that it���s not too much of an issue. However, Smalltalk tends to erase that distinction and there seems to be a solid community who are both user and developer and ���do brain surgery on themselves��� regularly. I am such a user and got surprised and a little damaged by this gotcha.

The thing is that the Set/Dictionary allSubInstances do: #rehash approach is extremely heavy-handed.

I agree. That would be one way to mitigate. I���m interested in others e.g. a code critic or warning in the browser like some refactoring have.