Apple's ability to release a Swift-based SDK that uses "final" and "final" being the default for classes in Swift are completely orthogonal concepts. Apple cou

Apple's ability to release a Swift-based SDK that uses "final" and "final" being the default for classes in Swift are completely orthogonal concepts. Apple could (and should, I think) release future SDKs that use all-final classes and require composition instead of the incredibly fragile base classes that currently make up UIKit and Foundation - they'd just add the "final" keyword. Since UIKit is inheritance-based currently, in a final-by-default Swift, it would be imported as "subclassable", "nonfinal", or whatever. Nothing would change other than the default for newly-written Swift code.