Observer.swift

var observers: [String: <#ObserverType#>] = [:]

func add(observer: <#ObserverType#>) -> String {
  let uuid = UUID().uuidString
  self.observers[uuid] = observer
  return uuid
}

func remove(observer uuid: String) {
  self.observers.remove(at: uuid)
}  

func notifyObservers(<#paramList#>>) {
  self.observers.forEach { $0.<#notifyMethod#> }
}