无法转换类型错误的值 - IOS

Question

我收到此错误：

  

无法转换类型'的值（（ObserveOnSerialDispatchQueueSink，   事件） - ＆gt;一次性）！”预期参数类型'（_） - ＆gt;   一次性'

以下是我的代码：

final fileprivate class ObserveOnSerialDispatchQueueSink < O: ObserverType >: ObserverBase < O.E > {
  let scheduler: SerialDispatchQueueScheduler
  let observer: O

  let cancel: Cancelable

  var cachedScheduleLambda: ((ObserveOnSerialDispatchQueueSink < O > , Event < E > ) - > Disposable) !

    init(scheduler: SerialDispatchQueueScheduler, observer: O, cancel: Cancelable) {
      self.scheduler = scheduler
      self.observer = observer
      self.cancel = cancel
      super.init()

      cachedScheduleLambda = {
        sink,
        event in
        sink.observer.on(event)

        if event.isStopEvent {
          sink.dispose()
        }

        return Disposables.create()
      }
    }

  override func onCore(_ event: Event < E > ) {
    let _ = self.scheduler.schedule((self, event), action: cachedScheduleLambda) //error
  }

  override func dispose() {
    super.dispose()

    cancel.dispose()
  }
}