Why write out the second convenience initializer for Car?

Greg:

The second convenience init, has a default property of 4 doors, that the super does not. And also, a convenience initializer can not be called from within another class, it must be called from within the same class.

He wrote this convenience init to illustrated how you can set default values. So when you create an instance of Car(), you have different options to choose from.

Hi Jhoan,

I may not have been clear. I'm talking about the second convenience initializer for Car, which is the third initializer overall:

convenience init() {
    self.init(name: "Unnamed")
}

This is the one that is identical to the superclass' init method. If we leave it out of the Car class definition, there is no impact that I can see. Check out the code below:

class Vehicle {

    var name: String

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

    convenience init() {
        self.init(name: "Unnamed")
    }

}

class Car: Vehicle {

    let numberOfDoors: Int

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

    convenience override init(name: String) {
        self.init(name: name, numberOfDoors: 4)
    }

    // not including the empty convenience init, because we've already inherited it

}

let car = Car()    // calling the inherited empty convenience init

car.numberOfDoors  // returns 4
car.name           // returns "Unnamed"

Additionally - to your point about not being able to call the superclass' convenience initializers - this is true if you're talking about calling it within the class definition. However, I'm talking about inheritance. You do inherit your superclass' convenience initializer, so long as you have implemented its designated initializer(s). From the docs:

Rule 2

If your subclass provides an implementation of all of its superclass designated initializers—either by inheriting them as per rule 1, or by providing a custom implementation as part of its definition—then it automatically inherits all of the superclass convenience initializers.

Greg :

You are right, I didn't see the other convenience initializer you were talking about until you pointed it out after. I thought you were talking about the one that sets the 4 doors by default. But yes, by inheriting from it's super class, my understanding is that he does inherits the convenience ini as well, unless I am wrong.

Would like to hear from Gabe Nadel himself.

Altho he did says in the video "Just for fun let's add another convenience initializer" probably to prove a point that you can have more than one convenience initializer.