问Swift类继承输出澄清

EN

class Car {
    var topSpeed = 200

    func drive() {
        print("Driving at \(topSpeed)")
    }
}

class Futurecar : Car {
    func fly() {
        print ("Flying")
    }
}


let myRide = Car() // Car
myRide.topSpeed // 200
myRide.drive() // Car

let myNewRide = Futurecar() // Futurecar
myNewRide.topSpeed // 200
myNewRide.drive() // Futurecar
myNewRide.fly() // Futurecar