Module observable 

Observable value wrapper with change notification and version tracking.

Design

Observable<T> wraps a value of type T in shared, reference-counted storage (Rc<RefCell<..>>). When the value changes (determined by PartialEq), all live subscribers are notified in registration order.

Performance

Operation	Complexity
get()	O(1)
set()	O(S) where S = subscribers
subscribe()	O(1) amortized
Memory	~48 bytes + sizeof(T)

Failure Modes

• Re-entrant set: Calling set() from within a subscriber callback will panic (RefCell borrow rules). This is intentional: re-entrant mutations indicate a design bug in the subscriber graph.
• Subscriber leak: If Subscription guards are stored indefinitely without being dropped, callbacks accumulate. Dead weak references are cleaned lazily during notify().

Structs

Observable

A shared, version-tracked value with change notification.

Subscription

RAII guard for a subscriber callback.