Shared state

Related Projects Swift Composable Architecture
3

Based on the responses in this post I've implemented shared state like this:

struct AppState: Equatable {
    var value: Value
    var homeState = HomeState()

    var homeValueState: SharedValueState<HomeState> {
        get {
            SharedValueState(value: value, state: homeState)
        }
        set {
            value = newValue.value
            homeState = newValue.state
        }
    }
}

struct HomeState: Equatable {
    var error: Error?
}

@dynamicMemberLookup
struct SharedValueState<State: Equatable>: Equatable {
    var value: Value
    var state: State

    subscript<LocalState>(dynamicMember keyPath: WritableKeyPath<State, LocalState>) -> LocalState {
        get { self.state[keyPath: keyPath] }
        set { self.state[keyPath: keyPath] = newValue }
    }
}

The Home reducer is of type Reducer<SharedGoalState<HomeState>, HomeAction, HomeEnvironment> and can operate on state.goal since the state is @dynamicMemberLookup.
Then the store in my view is var store: Store<SharedValueState<HomeState>, HomeAction>

With this, the source of truth for the Value instance is always the value member on AppState.