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iOS

Adam Teale
Adam Teale
10,989 Points
Posted by Adam Teale
Adam Teale
10,989 Points

calling function on type casted instance

Hey guys

I'm hoping that someone might be able to clear this up for me. I have one base class and two superclasses. I create an array that holds an instance of the base class and two instances of the superclasses. When I iterate this array I understood that each instance would be treated as the Base class (Animal). So why is it that in the for loop that each instance's "printName" function is called and not the Base "printName" function?

class Animal {
    var name: String
    init(_ name: String){s
        self.name = name
    }

    func printName(){
        print("Animal: \(self.name)")
    }
}

class Dog: Animal{
    override init(_ name: String){
        super.init(name)
    }

    override func printName(){
        print("Dog: \(self.name)")
    }

}

class Cat: Animal{
    override init(_ name: String){
        super.init(name)
    }

    override func printName(){
        print("Cat: \(self.name)")
    }
}

let k = Dog("k")
let j = Cat("j")
let a = Animal("a")

var animals = [k, j, a]

for p in animals{
    if let k = (p as? Animal) {
        p.printName()
    }

}

The printed output I get is:

Dog: k Cat: j Animal: a

I was expecting to see:

Animal: k Animal: j Animal: a

1 Answer

JLN CRML
JLN CRML
30,362 Points
JLN CRML
JLN CRML
30,362 Points

Whenever you override a method, the compiler will always execute the derived method. It has no access to the base class function, unless you call super. The array is indeed of type animal, but this is just to satisfy the compiler, in memory it may contain different instances of subclasses. An instance of a dog is basically a dog and an animal at the same time. For more information, I would recommend you looking up polymorphism.

JLN CRML
JLN CRML
30,362 Points
JLN CRML
JLN CRML
30,362 Points

One thing I should add is that you are not printing the casted instance in your code.