[Pitch #6] Actors

[kavon (Kavon Farvardin)]

@bjhomer

If we prohibit key-paths to actors, though, then it seems safe? So a key-path from an actor is fine, so long as it never goes to (or through ) another actor.

Yes this is the general problem: if the actor isolation of the accessed member does not match the actor-isolation of the context in which the subscript(keyPath:) is initially invoked, then it would require an async operation. Actors are currently the only area where async effects may arise while performing a lookup, but they may not be the only one in the future.