Normally optional requirements add an extra level of optionality:
- Methods become optional themselves (
f.bar?()) - Property getters wrap the value in an extra level of Optional (
if let bar = f.bar)
But there's nowhere to put that extra level of Optional for a property setter. That's really the entire story: we never figured out how to expose optional property setters in a safe way, and didn't want to pick any particular unsafe solution. If someone can think of something that'd be great!