WrappedStoreLocal.swift

// https://github.com/apple/swift-evolution/blob/main/proposals/0258-property-wrappers.md#delayed-initialization
@propertyWrapper
struct DelayedImmutable<Value> {
    private var _value: Value? = nil
    
    var wrappedValue: Value {
        get {
            guard let value = _value else {
                fatalError("property accessed before being initialized")
            }
            return value
        }
        
        // Perform an initialization, trapping if the
        // value is already initialized.
        set {
            if _value != nil {
                fatalError("property initialized twice")
            }
            _value = newValue
        }
    }
}

@propertyWrapper
struct WrappedStoreLocal<State, Action, LocalState>: DynamicProperty {
    @DelayedImmutable var wrappedValue: Store<State, Action>

    @DelayedImmutable @ObservedObject var projectedValue: ViewStore<LocalState, Action>

    @DelayedImmutable private var viewState: (State) -> LocalState
    @DelayedImmutable private var removeDuplicates: (LocalState, LocalState) -> Bool

    init(viewState: @escaping (State) -> LocalState, removeDuplicates: @escaping (LocalState, LocalState) -> Bool) {
        self.viewState = viewState
        self.removeDuplicates = removeDuplicates
    }

    init(viewState: @escaping (State) -> LocalState) where LocalState: Equatable {
        self.init(viewState: viewState, removeDuplicates: ==)
    }
    
    init(wrappedValue store: Store<State, Action>) {
        self.wrappedValue = store
        self.projectedValue = ViewStore(store.scope(state: viewState), removeDuplicates: removeDuplicates)
    }
}

struct AppState: Equatable {
    var string: String = .init()
    var int: Int = .init()
}

enum AppAction {}

struct MyView: View {
    struct ViewState: Equatable {
        var string: String

        init(state: AppState) {
            self.string = state.string
        }
    }

    @WrappedStoreLocal(viewState: ViewState.init) var store: Store<AppState, AppAction>

    var body: some View {
        Text($store.string)
    }
}

struct ParentView: View {
    @WrappedStore var store: Store<AppState, AppAction>

    var body: some View {
        MyView(store: <#T##Store<AppState, AppAction>#>) // what I'd like it to be
        MyView(store: <#T##WrappedStoreLocal<AppState, AppAction, MyView.ViewState>#>) // what it actually wants
    }
}