Inheritance in Swift

A class can inherit methods, properties, and other characteristics from another class. When one class inherits from another, the inheriting class is known as a subclass, and the class it inherits from is known as its superclass. A class that does not inherit from another class is known as a base class.

class someClass {
}

/** inheritting from someClass  **/
class someSubclass: someClass {
  //will have access to someClass properties
}

The above code snippet shows how the someSubclass inherited from the someClass class. Classes in Swift can call and access methods and properties belonging to their superclass and can provide their own overriding versions of those methods and properties to refine or modify their behavior. Classes can also add property observers to inherited properties in order to be notified when the value of a property changes.

Accessing Superclass Properties and Methods

Assuming we have a base class named Person and a Youtuber class that inherit from the Person class

class Person {
  let name: String
  var age: Int
  
  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }
  func celebrateBirthday() {
    self.age += 1
    print("Happy Birthday \(self.name)")
  }
}

class Youtuber: Person {
  let channelName: String
  var subscribers: Int
  
  //we need to pass in the name & age of the Youtuber Person
  init(channelName: String, subscribers: Int, name: String, age: Int) {
    self.channelName = channelName
    self.subscribers = subscribers
    
    //we use this to initialise the Person from within the subclass
    super.init(name: String, age: Int)
  }
}

The first thing I want us to notice is the class Youtuber: Person{}. We simply said the Youtuber be a type of Person which make it inherit all the properties and method of the Person class.

Secondly, when we initialize the Subclass, we use the super.init() method to pass the parameters needed by the superclass constructor since a Youtuber is actually still a Person.

We can access the celebrateBirthday() method of the Person class from the Youtuber subclass like below

Abel: Youtuber = Youtuber(channelName:"Swift",subscribers:32,name:"Abel",age:27)

Abel.celebrateBirthday() //Happy birthday Abel
Abel.age //27

Overriding Methods

At times, the subclass might wish to override a method contained in a superclass. We will make use of the override keyword within the subclass like below:

class Youtuber: Person {
  
  let channelName: String
  var subscribers: Int
  
  //we need to pass in the name & age of the Youtuber Person
  init(channelName: String, subscribers: Int, name: String, age: Int) {
    self.channelName = channelName
    self.subscribers = subscribers
    
    //we use this to initialise the Person from within the subclass
    super.init(name: String, age: Int)
  }
  
  /** This will override the celebrateBirthday in the superclass */
  override func celebrateBirthday() {
    self.age += 1
    print("Hi, happy birthday from ur youtube subscribers")
  }
  
}

Agoi: Person = Person(name: "Adeyemi", age: 27)
Agoi.celebrateBirthday() //Happy birthday Adeyemi

Abel: Youtuber = Youtuber(channelName:"Swift",subscribers:32,name:"Abel",age:27)
Abel.celebrateBirthday() //Hi, happy birthday from ur youtube subscribers

I initialized the Person class as well as the Youtuber class, the celebrateBirthday method in the Person class will return a different value to the Youtuber class because of the override function that print a different content in the Youtuber class.

Overriding Properties

we have seen how to override methods in swift, but there are cases where we actually need to override properties.

class Person {
  var name: String
  var gender: String = "Male"
  
  init(name: String) {
    self.name = name
  }
}

class Foreigner: Person {
  var country: String
  
  init(name: String, country: String) {
    
    super.init(name: name) //use to set the superclass initializer
    
    //change the default gender property 
    self.gender = "Female"
    self.country = country
  }
}

var newForeigner: Foreigner = Foreigner(name: "Johndoe", country: "Canada")
newForeigner.gender //will return Female since we already changed it in the init method

Immediately after the super.init() in the inside init method, we set the country variable. Note that, we can only do this after we have initialize the superclass.

Preventing Override

We can prevent a method or property from been overridden by a subclass by using the keyword final func or final var.

There is more to inheritance like observers. Didn’t cover that here because am not pretty sure how to use it now. Will update this article when I fully understand the concept. Lemme go read up enum and optionals. Yes, will write about it when done.

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