nested-closures.swift

// Can you tell which version has a retain cycle?

// Version A
class ViewControllerA: UIViewController {
    
    var workItem: DispatchWorkItem?
    
    override func viewDidLoad() {
        let workItem = DispatchWorkItem {
            UIView.animate(withDuration: 1.0) {
                self.view.backgroundColor = .red
            }
        }
        self.workItem = workItem
    }
}

// Version B
class ViewControllerB: UIViewController {
    
    var workItem: DispatchWorkItem?
    
    override func viewDidLoad() {
        let view = self.view
        let workItem = DispatchWorkItem {
            UIView.animate(withDuration: 1.0) { [weak self] in
                view?.backgroundColor = .red
            }
        }
        self.workItem = workItem
    }
}

// Version C
class ViewControllerC: UIViewController {
    
    var workItem: DispatchWorkItem?
    
    override func viewDidLoad() {
        let workItem = DispatchWorkItem {
            UIView.animate(withDuration: 1.0) { [weak self] in
                self?.view.backgroundColor = .red
            }
        }
        self.workItem = workItem
    }
}