Nil'ing AnyCancellable not cancelling subscription

Question

From the documentation

An AnyCancellable instance automatically calls cancel() when deinitialized.

Yet in the following code

    var cancellable: AnyCancellable?

    let subject: PassthroughSubject<Int, Never>? = PassthroughSubject<Int, Never>()

    cancellable = subject?.sink(receiveValue: {
        print("-> sending to cancellable \($0)")
    })

    print("send 1")
    subject?.send(1)


    // documentation states "An AnyCancellable instance automatically calls cancel() when deinitialized."
    print("cancellable nil'd")
    cancellable = nil

    print("send 2")
    subject?.send(2)

    print("send 3")
    subject?.send(3)

    DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(1)) {
        print("done")
    }

/*
send 1
-> sending to cancellable 1
cancellable nil'd
send 2
-> sending to cancellable 2
send 3
-> sending to cancellable 3
done
*/

Shows that nil'ing cancellable does not stop the subscriber from getting values.

While using a Set and removing all or nil'ing the set will stop the subscriptions. I even tried throwing everything into an autoreleasepool and it didn't do anything. Is the AnyCancellable in the code not getting deinitialized? Is something hanging on to it?

Test Playground

Playgrounds are notorious for hanging onto things with an extra reference so that they can display info about them. Try running this in a real app. — vacawama, Aug 25 '22 at 21:53
Do you want to put up an answer on how it works in an app but not in a playground? — Yogurt, Aug 25 '22 at 21:57

vacawama · Answer 1 · 2022-08-25T22:51:38.923

You are testing this in a Playground. The Swift Playgrounds are notorious for hanging on to objects with an extra reference so that you can interact with them in the Playground. This makes the Playground a poor choice for testing the allocation and freeing of objects.

Try this in a real app and you should find that it works as advertised.

Note: I have found that it will sometimes work out in a Playground if you put all of your code into a function (such as test()) and then call the function. That prevents variables at top level from being defined and hanging on to object references.

Nil'ing AnyCancellable not cancelling subscription

1 Answers1