Maybe that would have worked better with a metaclass.

But still, I think not using a metaclass is the more flexible design. Maybe I'll add the "add_slots" behavior into the @dataclass decorator in 3.10, even though it would need to return a new class. At least it could be well documented, and I doubt it's a concern for most people.

> Thanks for working on dataclasses :) - as I said, it's my #1 new feature in Python.

I'm offended! I also wrote f-strings, but maybe that's not considered new anymore. In any event, you're welcome!