Catalina compatibility tip: don’t use NSFont as a key in a Swift dictionary. I’m getting crashes from 10.15 users that include this message:
Fatal error: Duplicate keys of type ‘NSFont’ were found in a Dictionary. This usually means either that the type violates Hashable’s requirements, or that members of such a dictionary were mutated after insertion.
It’s quite possible this was always a bad idea, of course, and it’s just that in 10.15 it crashes. I don’t know.