NEW! Master Swift design patterns with my latest book! >>

< Previous: Class inheritance   Next: Final classes >

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!”.

Upgrade to premium

The Hacking with Swift guide book helps you learn faster, plus get an Xcode tips and tricks video and Swift wall chart.

< Previous: Class inheritance   Next: Final classes >
MASTER SWIFT NOW
Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Practical iOS 11 Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Click here to visit the Hacking with Swift store >>