Overriding methods

Child classes can replace parent methods with their own implementations – a process known as overriding. Here’s a trivial Dog class with a makeNoise() method:

class Dog {
    func makeNoise() {
        print("Woof!")
    }
}

If we create a new Poodle class that inherits from Dog, it will inherit the makeNoise() method. So, this will print “Woof!”:

class Poodle: Dog {
}

let poppy = Poodle()
poppy.makeNoise()

Method overriding allows us to change the implementation of makeNoise() for the Poodle class.

Swift requires us to use override func rather than just func when overriding a method – it stops you from overriding a method by accident, and you’ll get an error if you try to override something that doesn’t exist on the parent class:

class Poodle: Dog {
    override func makeNoise() {
        print("Yip!")
    }
}

With that change, poppy.makeNoise() will print “Yip!” rather than “Woof!”.