Method Reference Issue

MethodWeakCapture.swift

class CaptureClass {
    var action: ((Int) -> Void)?
  
    init() {
        // Passing a method reference to an escaping closure implicitly captures self
        // and in this case causes a refernce cycle!
        addAction(takesInt)
      
        // To avoid memory leak:
        addAction { [weak self] in self?.takesInt($0) }
    }
    
    func addAction(_ f: @escaping (Int) -> Void) {
        // store a strong ref to f, which might include a strong ref to a captured self
        action = f
    }
    
    func takesInt(_ i: Int) {}
    
    deinit {
        print("👍")
    }
}

var test = CaptureClass()
test = CaptureClass()

Hi Nils,
Thank you very much for your thoughts and great workarounds. Unfortunately I am not sure if they actually can help in the specific case I am facing using Combine.

I have attached a pseudo-code example and also added an idea for another workaround which unfortunately is not working:

import UIKit
import Combine

struct Presentation {
    let title: String
}

final class ViewModel {
    @Published private (set) var presentation = Presentation(title: "Some Title")
}

final class Proxy<T: AnyObject> {
    unowned let o: T

    init(original: T) {
        self.o = original
    }
}

final class NotReallyAViewController {
    let viewModel = ViewModel()
    var subscription: AnyCancellable?
    lazy var proxy = Proxy(original: self)

    func start() {
        // Causes retain cycle
        //subscription = viewModel.$presentation.sink(receiveValue: presentationDidChange)

        // All good but not so nice syntax
        subscription = viewModel.$presentation.sink(receiveValue: { [unowned self] in self.presentationDidChange(presentation: $0)})

        // Still a retain cycle
        //subscription = viewModel.$presentation.sink(receiveValue: proxy.o.presentationDidChange)
    }

    func presentationDidChange(presentation: Presentation) {
        print("presentationDidChange: \(presentation.title)")
    }

    deinit {
        print("☠️")
    }
}

var test: NotReallyAViewController? = .init()
test?.start()
test = nil

The proxy workaround was inspired by behaviour I observed in my code: I have a publisher on a view that is connected to a method on the view model, the subscription is stored in the view controller. This does not seem to cause a retain cycle. :thinking_face:

view.button.onTapPublisher.sink(receiveValue: viewModel.backAction)