Subclasses

A subclass is a class that inherits the functions from another class. You can do this using the extends keyword. Here is an example:

class Rectangle {    init(width, height) {        self.width = width        self.height = height    }
    area() { return self.width * self.height }}
class Square extends Rectangle { # Creating a subclass of Rectangle    init(length) {        super.init(length, length)    }}
var square = Square(30)print(square.area()) # The class inherits the method from its superclass

Here we are creating a subclass of Rectangle called Square. The square class's init func only takes one argument, unlike the rectangle one. But then it calls super.init(length, length). This is calling the init function of the rectangle class, initializing the self variables.

For safety reasons, if you define an existing superclass method in the subclass, it'll error. To override a superclass method in a sublass, you can put a override keyword infront of the method name. For example:

override [method name]([args]) {}