CODEWITHSUNDEEP
swiftios8
Nilzone-
Nilzone-

Reputation: 2786

Optionals in swift

I'm watching all the swift tutorials from Apple, but I'm having problems with one of the examples:

class Person {
    var residence: Residence?
}

class Residence {
    var address: Address?
}

class Address {
    var buildingNumber: String? = "234"
    var streetName: String? = "Main St."
    var appartmentNumber: String?
}

let paul = Person()
var addressNumber: Int?

addressNumber = paul.residence?.address?.buildingNumber?.toInt()

if let number = addressNumber {
    "correct"
} else {
    "fault"
}

It's always printing out "fault". Is there something painfully obvious I'm missing?

Upvotes: 0

Views: 203

Answers (4)

Firo
Firo

Reputation: 15566

Well you are never actually creating a valid Residence or Address, if you change your code to:

class Person {
    // actually create a residence object
    var residence: Residence? = Residence()
}

class Residence {
    // actually create a address object
    var address: Address? = Address()
}

class Address {
    // ...
}

let paul = Person()
var addressNumber: Int?

// Before Paul was never assigned a valid residence, now one will be created
addressNumber = paul.residence?.address?.buildingNumber?.toInt()

if let number = addressNumber {
    "correct"
} else {
    "fault"
}
// gives you `correct`

then it should work great!

Upvotes: 2

Craig Otis
Craig Otis

Reputation: 32054

Think it through, one step at a time. Particularly, your optional chaining:

addressNumber = paul.residence?.address?.buildingNumber?.toInt()

Ask yourself:

  1. What is paul?

  2. What is paul's residence property set to?

  3. What is the address of paul's residence?

Hint: You shouldn't make it past step 2.

Upvotes: 2

Brian Tracy
Brian Tracy

Reputation: 6831

let paul = Person()

You do nothing else to paul including setting his optional residence variable. So in the next line of code, you are accessing paul's residence which is nil.

addressNumber = paul.residence?.address?.buildingNumber?.toInt()
                      ^ failing right here, residence? returns nil

So with optional chaining, this entire expression returns nil, so when compared in your next if let statement, it is false. This is why the else clause is being executed.

Upvotes: 2

Cezary Wojcik
Cezary Wojcik

Reputation: 21845

You never initialize anything except Person(), so the residence property on paul is nil.

So, in the following optional chain:

addressNumber = paul.residence?.address?.buildingNumber?.toInt()
                              ^ you get nil here and don't continue

This means that addressNumber is nil.

Upvotes: 1

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