FREE: Follow my new 100 Days of Swift challenge! >>

< 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!”.

Sponsored You’re already busy updating your app for Swift 4.2 and iOS 12, so why not let Instabug help you find and fix bugs? Add just two lines of code to your project and receive comprehensive reports with all the feedback you need to ship a world-class app – click here to learn more!

< Previous: Class inheritance   Next: Final classes >
MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns 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 Advanced iOS Volume Two 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 >>