Swift vs. C# : Inheritance

• superclass/subclass (Swift/C#)

Defining a Base Class

Swift:

class Vehicle {

    var currentSpeed : Double = 0.0 {
         willSet(v) { println("Seeting \(v)") }
         didSet {  println("Now \(currentSpeed)") }
    }
    var speed: Double {
         get { return currentSpeed ; }
         set { currentSpeed = newValue; }
    }

    func makeNoise() {
        println("")
    }
}

C#

public class Vehicle {

    protected double currentSpeed = 0.0;

    public double Speed{
         get { return currentSpeed ; }
         set { 
            Console.Write("Setting"); Console.WriteLine(value);
            currentSpeed = value; 
            Console.Write("now "); Console.WriteLine(currentSpeed);
         }
    }

    public void MakeNoise() {
        Console.WriteLine("");
    }
}

Subclassing

Swift:

class Bicycle: Vehicle {
    var hasBasket = false
}

Bicycle().speed = 2.0

Seeting 2.0
Now 2.0

C#

public Bicycle : Vehcle {
   public bool hasBasket = false;
}

(new Bicycle()).Speed = 10.0


Setting10
now 10

Overriding

Swift:

• override キーワード

C#:

• new
• virtual / override

Accessing Superclass Methods, Properties, and Subscripts

Swift:

• super

C#:

• base

Overriding Methods

Swift:

class Bicycle: Vehicle {
    var hasBasket = false
    override func makeNoise(){
       println("Choo Choo");  
    }   
}

Bicycle().makeNoise() 

Choo Choo

C#

public class Bicycle : Vehicle {
   public bool hasBasket = false;
    public new void MakeNoise() {
        Console.WriteLine("Choo Choo");
    }
}

(new Bicycle()).MakeNoise();

Choo Choo

Overriding Properties

Overriding Property Getters and Setters

Swift: get/setともにoverride必要

class Bicycle: Vehicle {
    override var speed: Double { 
        get { return currentSpeed + 0.1; }
        set { super.speed = newValue; }
    }
}

println(Bicycle().speed)
Bicycle().speed = 10.9


0.1
Seeting 10.9
Now 10.9

C#:

public class Bicycle : Vehicle {
   public bool hasBasket = false;
   public new double Speed {
         get { return currentSpeed + 0.1; }
         set { base.Speed = value ; }
   }
}

Console.WriteLine( (new Bicycle()).Speed );
(new Bicycle()).Speed  = 10.9

0.1
Setting10.9
now 10.9

C#: superclassでvirtual宣言するとsetをoverrideしなくていよい

public class Vehicle {

    public virtual double Speed{
         get { return currentSpeed ; }
         set { 
            Console.Write("Setting"); Console.WriteLine(value);
            currentSpeed = value; 
            Console.Write("now "); Console.WriteLine(currentSpeed);
         }
    }
}

public class Bicycle : Vehicle {
   public override double Speed {
         get { return currentSpeed + 0.1; }
   }
}

Console.WriteLine( (new Bicycle()).Speed );
(new Bicycle()).Speed  = 10.9

0.1
Setting10.9
now 10.9

Overriding Property Observers

Swift:

class Car : Vehicle{
    override var currentSpeed: Double  {
         didSet {  println("Take care. \(currentSpeed)") }
    }   
}

Car().speed = 100.9

Seeting 100.9
Now 100.9
Take care. 100.9

Preventing Overrides

Swift: final

• overrideしようとするとコンパイルエラー

  • final var
  • final func
  • final class func
  • final subscript

class Car : Vehicle{

    final override func makeNoise() {
        println("*****")
    }
}

final class ImportCar: Car { 
    override func makeNoise() {
        println("@@@@@@")
    }
} 

./test2.swift:38:19: error: instance method overrides a 'final' instance method
    override func makeNoise() {

• サブクラスできない

  • final class

final class ImportCar: Car { } 
class AmericanCar: ImportCar { }


./test2.swift:35:7: error: inheritance from a final class 'ImportCar'
class AmericanCar: ImportCar { }

C# : sealed

public class Car : Vehicle {
    sealed public override double Speed{
        get { return base.Speed ; }
    }
}

public class AutomaticCar: Car{
    public override double Speed{
        get { return base.Speed ; }
    }
}


(2,28): error CS0239: `AutomaticCar.Speed': cannot override inherited member `Car.Speed' because it is sealed

sealed public class Car : Vehicle {}

public class AutomaticCar: Car{}

(1,15): error CS0509: `AutomaticCar': cannot derive from sealed type `Car'