KeyValueObservable.swift

protocol KeyValueObservable where Self: AnyObject {
    /// Stores all the added observations.
    var observationStore: ObservationStore<Self> { get }
    
    /// Sends key-value change notification to all the observers for this key path.
    func didChangeValue(for keyPath: PartialKeyPath<Self>)
    
    /// Adds observer for key path and returns observation token.
    /// - Note: Observation token is only useful if it is needed to remove observation before observer is deallocated. When observer is deallocated, then observation is removed when next key value change is handled.
    @discardableResult func addObserver<Observer: AnyObject, Value>(_ observer: Observer,
                                                                    keyPath: KeyPath<Self, Value>,
                                                                    options: Observation.Options,
                                                                    handler: @escaping (Observer, Value) -> Void) -> Observation
    
    /// Removes added observation.
    func removeObservation(_ observation: Observation)
}