PropertyObservers.swift

class Vehicle {
  var color: String?
  var maxSpeed = 80 {
    willSet(s) {
      print("Changing max speed from \(s)...")
    }
    didSet(s) {
      print("to \(s)")
    }
  }
  func description() -> String {
    return "A \(self.color) vehicle"
  }
  func travel() {
    print("Traveling at \(maxSpeed) kph")
  }
  deinit {
    print("AAaaaaaaaa!!!!")
  }
}