CODEWITHSUNDEEP
swiftself
Andrew Breeze-Stringfellow
Andrew Breeze-Stringfellow

Reputation: 3

Why is self used with init but not colour

I am taking an online class on swift and an example was shown. Why is self used with the init method call but not on colour?

class Car {

    var colour = "Black"
    var numberOfSeats = 5
    var typeOfCar : CarType = .Coupe

    init() {

    }

    convenience init (customerChosenColour : String) {
        self.init()
        colour = customerChosenColour
    }
}

Upvotes: 0

Views: 89

Answers (2)

Ricky Mo
Ricky Mo

Reputation: 7718

As you wonder why self. cannot be omitted in self.init(), you can think of self.init() as whole is a special keyword just for convenience initializer. Same as super.init() as whole is a special keyword just for designated initializer. And Car.init()aka Car() is for creating a new instance. Calling init() itself without any receiver is not a valid call ever. So you can treat function call init() as nonexistence, self.init() is one keyword, super.init() is another keyword.

init() is not a member function, it is the initializer, some special code which will be run when creating new instances of that class. Don't treat initializers as regular member functions. They don't have the func keyword in front. They don't have the property of member functions. You can call member function on an instance but you cannot call initializer on an instance (Car().init() is not valid). self.init() dose NOT mean calling a function named init() from self.

class Foo
{
    init(){}

    func foo(){}

    func bar()
    {
        self.foo()  //valid. regular member function call
        self.init() //invalid. init() is not a member function of the instance
    }
}

Don't think self.init() like calling regular method from the same class, where self. can be omitted, but rather treat the whole thing as a special keyword that means "initialize this object with the designated initializer first".

Upvotes: 0

user10826856
user10826856

Reputation:

An init() runs when someone makes a new instance of that class like this:

var newInstanceOfCar = Car()

A convenience init allows you to create other initializers for certain use cases, like when there is a customerChosenColour that needs to be specified. It makes things more convenient in those cases.

The reason why self is used, is because when you create convenience init, you still need to call the "main" init, which is a property of self.

You can use self on colour, but it isn't necessary. You would use self.colour, if colour was ambiguous, like in this example:

class Car {

    var colour = "Black"
    var numberOfSeats = 5
    var typeOfCar : CarType = .Coupe

    init() {

    }

    convenience init (colour : String) {
        self.init()
        self.colour = colour
    }
}

Notice how colour is a property of Car, but is also the name of the parameter for the convenience init. It would be confusing to write colour = colour.

So we use self to say that we want the variable in our class, self.colour, to be equal to the value of the parameter, colour.

Upvotes: 1

Related Questions