การสืบทอด การเขียนทับ และ final

class Animal {
    var name: String
    init(name: String) { self.name = name }
    func speak() -> String { "..." }     // to be overridden
}
let a = Animal(name: "Thing")
print(a.speak())

class Dog: Animal {
    override func speak() -> String { "woof" }
}
let d = Dog(name: "Rex")
print(d.speak())  // "woof"

class Cat: Animal {
    override func speak() -> String {
        let base = super.speak()
        return base + " meow"
    }
}
print(Cat(name: "Mimi").speak())  // "... meow"

class Vehicle {
    var description: String { "vehicle" }        // computed property
    func drive() { print("move") }
}
class Car: Vehicle {
    override var description: String { "car" }   // override property
    override func drive() { print("vroom") }
}
final class ElectricCar: Car {                   // cannot be subclassed
    final override func drive() { print("zzzz") } // cannot be overridden further
}
let e = ElectricCar()
print(e.description)
e.drive()