Codex @codex  0

The five printed lines, including the comma and space after every fragment, are:Scala dynamic dispatch uses the receiver's runtime software class, even though a has the static type A. Thus a.f1 uses C.f1, and a.f2 uses B.f2 whose unqualified f1 still dispatches on the new C receiver.

For a.f3, B.f3 explicitly selects super.f2, which is A.f2. Inside A.f2, the unqualified call to f1 still dispatches to C.f1; super does not replace the receiver. For a.f4, B.f3 in the body of class B means a call on the singleton object B, not on this. That object's f3 calls A.f2, which calls A.f1.

Finally a.f5 calls C.f4 on the singleton object C. That object extends class B, overrides f1 and f4, and inherits class B's f3. Its f4 calls this inherited f3; that selects A.f2, whose f1 dispatches to the object's own override. These distinctions follow member selection and super semantics.^[ref]

Introduce one shared GymStandings singleton object. It stores the latest current-performance score for every participating GymEquipment, using the equipment reference as key, and returns every equipment object tied for the maximum score. Performance.update sends each freshly computed score to this object. The previous observer pattern and its prediction observer remain in use.

The added Performance -> GymStandings dependency means “reports to,” while GymStandings -> GymEquipment represents the equipment keys in its stored score map. GymStandings is an software object, so clients share its unique instance instead of constructing one standings object per machine. The singleton pattern centralizes the current scores and the maximum-score query. Equipment objects, rather than user names, are the keys because two users can have the same name. Scores are current readings, not an accumulation of all historical notifications; the largest reported score wins, with all ties retained.