Swift Multiple Inheritance. I am trying to recreate this Java Code in Swift related to Multiple Inheritance

Question

public class Shape {
     public static void main (String[] args) {
    

        Circle c = new Circle(5);
        System.out.println (c.getArea());
        c.setColour("Green");
        System.out.println (c.getColour());

  
    }
}

    interface Colour {
        String getColour();
        void setColour (String colour);
    }

    abstract class Shapes implements Colour {
        abstract double getArea();
        private String colour = "Red";

    public String getColour() {
        return colour;
    }
    public void setColour(String colour) {
        this.colour = colour;
    }

}
class Circle extends Shapes {
    private int radius;

    public Circle(int radius) {
    this.radius = radius;
}



    public double getArea() {
        return Math.PI * radius * radius;
    }
}

I have attempted a Swift Solution the code is below

import Cocoa

protocol Colour {
    var colour: String { get set }

    func getColour() -> (String)
    func setColour(colour: String)

}

class Shape: Colour {
    var colour: String = "Red"

    init(colour: String) {
        self.colour = colour
    }

    func getColour() -> (String) {
        return colour
    }

    func setColour(colour: String) {
        self.colour = colour
    }

    func getArea() -> Double {
        return 0.0
    }



}

class Circle: Shape {
    let radius: Double


    init(radius: Double) {
        self.radius = radius
    }

    override func getArea() -> Double {
        return radius * radius * Double.pi
    }


   }

I have written code to create an interface 'colour', a super class 'shape' and a subclass 'Circle'. The aim is to learn more about inheritance and multiple inheritance as a new programmer. The java code works as intended.

But i am getting an error " 'super.init' isn't called on all paths before returning from initializer" with the above Swift code. As I am newer to swift and multiple inheritance I am not sure how to correct this error.

How I can correct this?

Answer 1

Your error is related to the initialization of superclasses. Whenever you inherit the superclass, to initialize it you must write super.init() on the first line of the Circle class's initializer.

//Inside of Circle class

 init(radius: Double) {
//I've initialized shape using the color Red, but you can use any string.
        super.init(color: "Red")
        self.radius = radius
    }

Answer 2

Neither Swift nor Java support multiple inheritance.

C++ does, and a few others.

In Swift you can use protocols to accomplish very similar things, but conforming to a protcol is not the same thing as inheriting from a parent class.

Your problem is that your initializer needs to call its parent class' initializer:

init(radius: Double, color: String) {
    self.radius = radius
    super.init(color: color)
}

(Circle needs to call super.init, or in this case, init(colour:) from its shape superclass.)

Note that your circle shape's initializer should probably take a color as well as a radius: