Version 9.0 beta 6 (9M214v)
MyHostObject owns MyObject and observes changes of it's value:
With Objective-C equivalent, MyHostObject would still be able to remove observation from myObject.
This is happening because NSKeyValueObservation holds a weak reference to an object. That weak reference turns to nil too soon. My suggestion is to use unowned or Unmanaged<MyObject> reference.