Comment by phailhaus

That's only for dataclasses, you can't implement your own class like this without implementing it as a dataclass, because the typechecking for it is hacked in as a custom plugin.

What I'm trying to point out is that these features exist in core Python and yet the type system they built can't express it. By contrast, TypeScript is designed in such a way that you can implement everything yourself without having to write "custom typescript checker plugins".