How to use Codable to store preferences in Swift

Issue #462

Using object, we don’t need to care about nil vs false like in UserDefaults, our object is the source of truth

class StoringHandler<T: Codable> {
    private let key: Storage.Keys
    private let storage = Deps.storage

    init(key: Storage.Keys) {
        self.key = key
        load()
    }

    var object: T? {
        didSet {
            if let object = object {
                try? storage.save(object: object, key: key)
            } else {
                try? storage.clear(key: key)
            }
        }
    }

    private func load() {
        self.object = try? storage.load(key: key, as: T.self)
    }
}

Then subclass StoringHandler

struct OnboardInfo: Codable {
    let hasOnboarded: Bool
}

final class OnboardingHandler: StoringHandler<OnboardInfo> {
    let storage = Deps.storage

    var hasOnboarded: Bool {
        get {
            return object?.hasOnboarded ?? false
        }
        set {
            object = OnboardInfo(hasOnboarded: newValue)
        }
    }
}