How do I create a subclass with additional property that is not set to default?

Hey Łukasz Kozaczkiewicz,

The purpose of the init method is to make sure all the object's properties have values (nil is acceptable and the default value for all optional types).

When subclassing, you must:

1. Initialize all the properties of the subclass
2. initialize the properties inherited from the superclass using super.init

It's important that you do these things in this order. You can't call the initializer of the superclass until all the properties of the subclass are initialized.

class Vehicle {
    var numberOfWheels: Int

    init(numberOfWheels: Int) {
        self.numberOfWheels = numberOfWheels
    }
}

class Car: Vehicle {
    var numberOfDoors: Int

    init(numberOfDoors: Int, numberOfWheels: Int) {
        self.numberOfDoors = numberOfDoors
        super.init(numberOfWheels: numberOfWheels)
    }
}

Good Luck

Hey Steven, Thank you for your answer. It is all clear now. The reason I was confused was the treehouse tutorial - overriding properties, in which the override init method was shown. This is something I still don't understand :-Z The approach you shown is way easier. Thx again