Tasks always seem to run in order in Swift code

This code always seems to work like magic. Without any locking, the output is 1,2.

class Counter {
    var count = 0
    func increment() -> Int {
        count += 1
        return count
    }
}

class ViewController: UIViewController {
    
    var tasks = [Task<Void, Never>]()

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let counter = Counter()
        
        tasks += [
            Task.detached {
                print(counter.increment())
            }
        ]

        tasks += [
            Task.detached {
                print(counter.increment())
            }
        ]
    }
}

This code is from https://www.andyibanez.com/posts/understanding-actors-in-the-new-concurrency-model-in-swift/

I'm expecting it to work inconsistently. I've tried switching it to not use detached tasks, but still it always returns 1,2. What is going on?

Solution

First, on Simulator, this only uses a single thread (*), so you won't see it get out of order with this code. On device, it uses multiple threads, but you probably won't see it out of order very often for just 2 tasks. If you re-write this with 100 tasks and run on device, it's very easy to show what you're looking for.

    for _ in 1...100 {
        tasks += [
            Task.detached {
                print(counter.increment())
            }
        ]
    }

(*) I've been told by folks I trust that Simulator uses 2 threads, at least now (I haven't run tests to check). This still causes the same symptom, since one is dedicated to main.