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iOS Object-Oriented Swift 2.0 Class Inheritance Creating a Subclass

Posted by Todd Stacy
Todd Stacy
5,816 Points

initializer help please

i think im just bad at reading directions or something. i understand everything in the videos, but i have no idea why im getting an error on line 23. the comments are other tries that failed also. it says im missing an argument in the call.

classes.swift 
class Vehicle {
    var numberOfDoors: Int
    var numberOfWheels: Int

    init(withDoors doors: Int, andWheels wheels: Int) {
        self.numberOfDoors = doors
        self.numberOfWheels = wheels
    }
}

// Enter your code below
class Car: Vehicle {

    let numberOfSeats: Int  

    override init(withDoors doors: Int, andWheels wheels: Int) {
        super.init(withDoors: doors, andWheels: wheels)
        self.numberOfSeats = 4 

    }
}

//let someCar = Car(withDoors: Int, andWheels: Int)
//let someCar = Car(doors: Int, wheels: Int)
let someCar = Car(withDoors doors: Int, andWheels wheels: Int)

1 Answer

Steven Deutsch
Steven Deutsch
21,046 Points
Steven Deutsch
Steven Deutsch
21,046 Points

Hey Todd Stacy,

Let me see if I can clear a few things up for you. First, this is a scenario where you don't need an initializer for your Car subclass. The purpose of an initializer is to make sure all of an objects properties have values when it is created. The challenge asks you to assign a default value for the numberOfSeats property. This means, to create an instance of Car, you just have to call the initializer of the parent class, because all the properties of the Car class that are not being inherited already have values.

class Vehicle {
    var numberOfDoors: Int
    var numberOfWheels: Int

    init(withDoors doors: Int, andWheels wheels: Int) {
        self.numberOfDoors = doors
        self.numberOfWheels = wheels
    }
}

// Enter your code below

class Car: Vehicle {
  var numberOfSeats = 4
}

let someCar = Car(withDoors: 4, andWheels: 4)

Second, remember how I just said that the job of an initializer is to make sure the objects properties are set with values? This means when you call the initializer, you have to pass it the values of the expected type to populate the properties. You were trying to pass in types and not actual values. The types are already defined in the class itself.

Also, the reason why we use withDoors and andWheels when calling the initializer is because these are external parameter names that have been specified. Remember, functions (initializers) have local parameter names and external parameter names. If the external name is not specified, the local name will be used as the external name. However, if an external name is specified, it has to be used when making the function call.

Good Luck