...
          Provider(
            observing: { navigator, currentScreenID in
              DetailViewModel(
                train: screen.train,
                navigator: navigator,
                currentScreenID: currentScreenID
              )
            },
            content: { viewModel in
              DetailView(viewModel: viewModel.vm)
            }
          )
...

class DetailViewModel: ObservableObject {
  let train: Train
  let navigator: Navigator
  let currentScreenID: ScreenID

  @Published var counter: Int = 0

  init(train: Train, navigator: Navigator, currentScreenID: ScreenID) {
    self.train = train
    self.navigator = navigator
    self.currentScreenID = currentScreenID
  }

  func increaseCounter() {
    counter += 1
  }

  func decreaseCounter() {
    counter -= 1
  }

  func showCapacity() {
    navigator.go(
      to: CapacityScreen(capacity: train.capacity),
      on: currentScreenID
    )
  }

 struct ValueTypeVM {
    let counter: Int
    let train: Train
    let increaseCounter: () -> ()
    let decreaseCounter: () -> ()
    let showCapacity: () -> ()
  }

  var vm: ValueTypeVM {
    ValueTypeVM(
      counter: counter,
      train: train,
      increaseCounter: self.increaseCounter,
      decreaseCounter: self.decreaseCounter,
      showCapacity: self.showCapacity
    )
  }
}