How to invalidate timer in extension in Swift

Question

I was trying to add a timer property in an extension. The code is as follow

 @objc public extension RCTTouchHandler {
  static let kSessionTimer = "sessionTimer"
  
   var sessionTimer: Timer {
    get {
      return objc_getAssociatedObject(self, RCTTouchHandler.kSessionTimer) as? Timer ?? Timer.scheduledTimer(timeInterval: RCTTouchHandler.kSessionExpiredDuration, target: self, selector: #selector(touchSessionExpiration), userInfo: nil, repeats: false)
    }

    set(timer) {
      objc_setAssociatedObject(self, RCTTouchHandler.kSessionTimer, self, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
  }

  @objc func touchSessionExpiration() {
    print("session expired")
  }

  deinit {
    self.sessionTimer.invalidate()
  }
}

Then,sessionTimer has strong reference to this object, in the meantime, this object strongly retains sessionTimer. To avoid retain-cycle and memory leak, I should invalid the timer when the object is deinitialized. But, I encountered the following error when trying to invalidate the timer in the deinit func in this extension.

Deinitializers may only be declared within a class 

According to Swift Doc

Extensions can add new convenience initializers to a class, but they cannot add new designated initializers or deinitializers to a class. Designated initializers and deinitializers must always be provided by the original class implementation.

So I am wondering how should I invalidate the timer properly in this extension?

Answer 1

As you stated, you cannot implement deinit { } in extensions.

---

You could create your own object and implement deinit { } there and instead of using RCTTouchHandler everywhere, use your own object:

@objc extension RCTTouchHandler {
    static let kSessionTimer = "sessionTimer"
}

public class MyTouchHandler: RCTTouchHandler {
    private var timer: Timer? = nil

    var sessionTimer: Timer {
        get {
            guard let timer = timer else {
                let newTimer = Timer.scheduledTimer(timeInterval: RCTTouchHandler.kSessionExpiredDuration, target: self, selector: #selector(touchSessionExpiration), userInfo: nil, repeats: false)
                self.timer = newTimer
                return newTimer
            }
            return timer
        }

        set(timer) {
            self.timer = timer
        }
    }

    @objc func touchSessionExpiration() {
        print("session expired")
    }

    deinit {
        self.timer?.invalidate()
    }
}