I think I’ll just add an extreme to the docs. The behaviour makes sense to me now, it’s just that i didn’t form the right model from reading the docs. So helping the reader to form the right model would likely resolve the issue without having to modify the code. I’ll take a stab at it next week, hopefully

is there any way of copying a class object into a new one with some (non-init fields) updated to new values in the same way there is struct-copy?

Specifically from inside the class. I’d like a updated-copy-of-self type method

I haven’t understood all the details of Roaring Bitmaps, but have you looked at data/integer-set? https://docs.racket-lang.org/data/integer-set.html