Is there any way to specify a generic type which is constrained to either a type or an optional type?

[anandabits (Matthew Johnson)]

@gwendal.roue

Start from the beginning: the only expressible constraints for generic types in Swift are protocol conformances, subclassing, and combination of those

For now. My pitch for generalized supertype constraints was well received. We just can't move it forward until somebody volunteers to work on implementation. If / when that happens the compiler would recognize the Bool: Bool? relationship in a generic constraint.

@gwendal.roue

Swift won't let you restrict Boolish conformance on Bool and Bool? only, though. You may have to explicitly document that no other types should adopt this protocol.

Also for now. Hopefully we can express closed protocols in the language eventually. This has been the topic of several threads in the past.