Protocol requirements co/contra variance

[Jumhyn (Frederick Kellison-Linn)]

Old (but relevant) thread from a couple years back:

Protocol Witness Matching Mini-Manifesto

Hello Swift community, I have been working on a "mini-manifesto" whose aim is to set out basic design principles around protocol witness matching and get some agreement from the Swift community on it. One of the reasons why is because I am currently pitching a new form of witness matching and while we've had some discussion on this forum on different kinds of matching (like subtyping, etc), it would be great to have a small document which people can refer to during discussions and use it to cre…