Inheritance

Defining a Base Class

                  class Vehicle {

    var currentSpeed = 0.0

    var description: String {

        return "traveling at \(currentSpeed) miles per hour"

    }

    func makeNoise() {

        // do nothing - an arbitrary vehicle doesn't necessarily make a noise

    }

}
                

                  let someVehicle = Vehicle()
                

                  print("Vehicle: \(someVehicle.description)")

// Vehicle: traveling at 0.0 miles per hour
                

Subclassing

                  class SomeSubclass: SomeSuperclass {

    // subclass definition goes here

}
                

                  class Bicycle: Vehicle {

    var hasBasket = false

}
                

                  let bicycle = Bicycle()

bicycle.hasBasket = true
                

                  bicycle.currentSpeed = 15.0

print("Bicycle: \(bicycle.description)")

// Bicycle: traveling at 15.0 miles per hour
                

                  class Tandem: Bicycle {

    var currentNumberOfPassengers = 0

}
                

                  let tandem = Tandem()

tandem.hasBasket = true

tandem.currentNumberOfPassengers = 2

tandem.currentSpeed = 22.0

print("Tandem: \(tandem.description)")

// Tandem: traveling at 22.0 miles per hour
                

Overriding Methods

                  class Train: Vehicle {

    override func makeNoise() {

        print("Choo Choo")

    }

}
                

                  let train = Train()

train.makeNoise()

// Prints "Choo Choo"
                

Overriding Property Getters and Setters

                  class Car: Vehicle {

    var gear = 1

    override var description: String {

        return super.description + " in gear \(gear)"

    }

}
                

                  let car = Car()

car.currentSpeed = 25.0

car.gear = 3

print("Car: \(car.description)")

// Car: traveling at 25.0 miles per hour in gear 3
                

Overriding Property Observers

                  class AutomaticCar: Car {

    override var currentSpeed: Double {

        didSet {

            gear = Int(currentSpeed / 10.0) + 1

        }

    }

}
                

                  let automatic = AutomaticCar()

automatic.currentSpeed = 35.0

print("AutomaticCar: \(automatic.description)")

// AutomaticCar: traveling at 35.0 miles per hour in gear 4