AppStorage part 2

Turns out this topic needs more than just one post. In part 1, I described how I was able to use AppStorage for an enum with associated values.

Here I will discuss a challenge I encountered when attempting to build the View to enable users to change their value for the languageChoice enum.

enum LanguageChoice: Equatable, Codable {
    case all
    case oneToOne(Language, Language)
    case oneToAll(Language)
    case allToOne(Language)
    case symmetricSubset(Set<Language>)

Step 1, create a version of LanguageChoice with no associated values:

    enum SimpleLanguageChoice: String, CaseIterable {
        case all
        case oneToOne
        case oneToAll
        case allToOne
        case symmetricSubset
    }

Step 2, create a state variable using the new enum type and bind it to a picker:

    @State var languageChoice: SimpleLanguageChoice = .all
    var body: some View {
        VStack {
            Picker("Languages Choice", selection: $languageChoice) {
                ForEach(SimpleLanguageChoice.allCases, id: \.self) {
                    Text($0.rawValue)
                        .tag($0)
                }
            }
        }
    }

Step 3, add UI below the picker to display the appropriate controls to go with the value of languageChoice.

    @ViewBuilder var bottomStuff: some View {
        switch languageChoice {
        case .all:
            EmptyView()
        case .oneToAll:
            Picker("Ask in", selection: $language) {
                ForEach(Language.allCases, id: \.self) {
                    Text($0.rawValue)
                        .tag($0)
                }
            }
     // et cetera

Step 4, add an AppStorage var to get the persisted LanguageChoice value and use it to configure the Picker UI.

    @AppStorage("languageChoice") var persistedLanguageChoice: LanguageChoice = .all
    @State var languageChoice: SimpleLanguageChoice

init() {
     languageChoice = SimpleLanguageChoice.simpleChoice(for: persistedLanguageChoice)
}

Insert record scratch sound here! This code created the following compiler error:
'self' used before all stored properties are initialized

I wanted to use the persisted languageChoice to set up the UI to allow users to choose a new languageChoice. But doing this required reading persisted languageChoice, which was not allowed. Alas. So to get things to work I needed to set a default value for languageChoice in the declaration and then update the value in init. Just do this, right?

    @State var languageChoice: SimpleLanguageChoice = .all
    init() {
        languageChoice = SimpleLanguageChoice.simpleChoice(for: persistedLanguageChoice)

Nope. If you set an initial value for a State variable in the declaration, updating it in init gets more complicated. You need to do this:

    init() {
        _languageChoice = State(initialValue: SimpleLanguageChoice.simpleChoice(for: persistedLanguageChoice)