Sharing states between domains?

[nicnocquee]

Hello,

I wonder if anyone can give suggestions on how to share a state between domains?

From this episode-code-samples,

struct AppState: Equatable {
  var count = 0
  var favorites: Set<Int> = []

  var counter: CounterState {
    get {
      .init(count: self.count, favorites: self.favorites)
    }
    set {
      self.count = newValue.count
      self.favorites = newValue.favorites
    }
  }
  var profile: ProfileState {
    get {
      .init(favorites: self.favorites)
    }
    set {
      self.favorites = newValue.favorites
    }
  }
}

the favourites is duplicated in three places: AppState, CounterState, and ProfileState. Is this really the recommended way?

[stephencelis]

While it may look like favorites is duplicated 3 places, AppState.counter and AppState.profile are computed properties that use AppState.favorites under the hood. This means there's really only a single favorites field in state, and not 3, so there's no way for AppState.favorites, CounterState.favorites, or ProfileState.favorites to ever fall out of sync. They all use the same single field as a backing store under the hood.

There is boilerplate involved in managing these computed sub-sets of state, but it's typically the same amount of code (or less) than equivalent code that manually coordinates state between components.

[nicnocquee]

I see. Thanks for the clarification! Love TCA, btw 👍