@MainActor @Observable final class TickerODMO {
   private(set) var tick: Int = 0
   @ObservationIgnored private var tickerTask: Task<Void, Error>?

   func startTicking() {
      guard tickerTask == nil else { return }
      tickerTask = Task {
         while !Task.isCancelled {
            try await Task.sleep(for: .milliseconds(500))
            tick += 1
         }
      }
   }

   func stopTicking() {
      tickerTask?.cancel()
      tickerTask = nil
   }
}

@MainActor func observe(ticker: TickerODMO) async throws {
   let observations = Observations { ticker.tick }
   print("creating observer task 1")
   let task1 = Task {
      for await tick in observations {
         print("task 1 observed tick=\(tick)")
      }
   }
   print("starting ticker and sleeping for 2 seconds")
   ticker.startTicking()
   try await Task.sleep(for: .seconds(2))
   print("cancelling task 1, then sleeping for 3 seconds")
   task1.cancel()
   try await Task.sleep(for: .seconds(3))
   print("creating observer task 2")
   let task2 = Task {
      for await tick in observations {
         print("task 2 observed tick=\(tick)")
      }
   }
   try await Task.sleep(for: .seconds(3))
   task2.cancel()
   ticker.stopTicking()
}