ARC(Automatic Reference Counting) in Action

Question

I am currently following the Apple Documentation. Here is my question:

class Person {
    let name: String
    init(name: String) {
        self.name = name
        println("\(name) is being initialized")
    }
    deinit {
        println("\(name) is being deinitialized")
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        var reference1: Person?
        var reference2: Person?
        var reference3: Person?
        reference1 = Person(name: "John Appleseed")
        // prints "John Appleseed is being initialized
        reference2 = reference1
        reference3 = reference1

        reference1 = nil
        reference2 = nil
    }
}

After reference1 equals nil, ARC deallocates the instance and prints "John Appleseed is being deinitialized"

Should not it be deallocates after reference3 = nil?

Answer 1

The problem here is a matter of scope. We can find out more with breakpoints.

Here, we are stopped just before we initialize reference1.
All variables are expectedly nil:

And after the initialization of reference1?

---

Okay, let's skip forward to after reference2 and reference3 are set:

All three variables point to the same memory location, and we can see the initializer only ran once. These all point to the same location.

Let's step forward:

reference1 is now pointing to None. It is nil. The deinit mmethod has not been called and printed its message.

Let's step forward some more:

Now reference1 and reference2 are both expectedly nil. The println statements I've added were called. But deinit did not run and reference3 is not nil.

The next step is stepping all the way out of the method. Once we're out of the method, the variables are out of scope and the deinit is called: