Feedback to next generation APIs #668

This is the issue to discuss the defaults and behavior of attr.define(), attr.mutable(), and attr.frozen() before they are finalized inside the new attrs namespace.

Feedback that we find justified will be spun out into separate issues.

Known issues:

• mypy doesn't know about the new-style APIs yet and there's nothing we can do about it. However you can use this mypy plugin for now (for more details see https://www.attrs.org/en/stable/extending.html#wrapping-the-decorator). PR is submitted in Add support for next-gen attrs API python/mypy#9396.
• __eq__ and __ne__ aren't correctly auto-detected (fixed) @attr.define fails to auto-detect __eq__ #670
• Unannotated attributes fail if define is called with arguments/parantheses (fixed) Hybrid behavior doesn't work when maybe_cls=None and no annotations #673
• Inheriting from frozen classes requires to manually set on_setattr to None (fixed). Feedback to next generation APIs #668 (comment))