ReferencesBag.swift

class ReferencesBag {
    
    private var references: [AnyObject] = []
    
    func append(_ reference: AnyObject) {
        references.append(reference)
    }
}

// For details about Token class please visit this address :
// https://github.com/objcio/S01E27-typed-notifications-part-1/blob/master/Typed%20Notifications%20(Part%201).playground/Pages/Typed%20Notifications%20(Part%201).xcplaygroundpage/Contents.swift
extension Token {
  
    func disposed(by referencesBag: ReferencesBag) {
        referencesBag.append(self)
    }
}

class FeedViewController {
    
    private let referencesBag = ReferencesBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupApplicationNotifications()
    }
  
    private func setupApplicationNotifications() {
        NotificationCenter.default
            .addObserver { [feedViewModel] (notification: ApplicationWillEnterForegroundNotification) in
                feedViewModel.willEnterForeground()
            }
            .disposed(by: referencesBag)
    }
}