'/' is deprecated: Use a 'CasePathable' case key path, instead.

[3a4oT]

Hello, I have a warning on a higher order reducer that says '/' is deprecated: Use a 'CasePathable' case key path, instead.

@Reducer
public struct AnalyticsReducer<State, Action>: Sendable, Reducer where Action: AnalyticsTrackableAction {
    @Dependency(\.analyticsClient) private var analyticsClient
    public init() {}
    public func reduce(into state: inout State, action: Action) -> Effect<Action> {
        guard let event: AnalyticsEvent = (/Action.analyticsTrack).extract(from: action) else {
            return .none
        }
        return .run { _ in
            await analyticsClient.track(event)
        }
    }
}

How can I refactor (/Action.analyticsTrack).extract(from: action) to use CasePathable?

Swift 5.10

[stephencelis]

The AnalyticsTrackableAction protocol needs to encode its ability to extract analyticsTrack actions.

The simplest would be to add a getter for the extraction:

 protocol AnalyticsTrackableAction {
   static func analyticsTrack(_ event: AnalyticsEvent) -> Self
+  var analyticsTrack: AnalyticsEvent? { get }
 }

Conforming enums would get this for free if you mark them with @dynamicMemberLookup:

+@dynamicMemberLookup
 @CasePathable enum Action: AnalyticsTrackableAction {
   case analyticsTrack(AnalyticsEvent)
 }

And then you would update your reducer operator:

-guard let event: AnalyticsEvent = (/Action.analyticsTrack).extract(from: action) else {
+guard let event: AnalyticsEvent = action.analyticsTrack else {

The alternative would be to constrain the protocol to CasePathable with an additional protocol constraint on AllCasePaths:

protocol AnalyticsTrackableAction: CasePathable
where AllCasePaths: HasAnalyticsEventCasePath<Self> {}

protocol HasAnalyticsEventCasePath<Root> {
  associatedtype Root: CasePathable
  var analyticsEvent: AnyCasePath<Root, AnalyticsEvent> { get }
}

And in practice you would need to extend both the action and its AllCasePaths type to the protocols for the conformance to work:

@CasePathable enum Action: AnalyticsTrackableAction {
  case analyticsEvent(Bool)
}
extension Action.AllCasePaths: HasAnalyticsEventCasePath {}

Note that in Swift <6 this extension needs to live in a separate file due to a bug with macros that was fixed in Swift 6.

[3a4oT]

Did you try adding the conformance in an extension instead? Possibly in a different file even?

Enum 'case' is not allowed outside of an enum - so you can't add the conformance in an extension.

That was my bad! I was under the impression this worked and that we'd taken advantage of it elsewhere, but I'm mistaken. I think that unfortunately the other protocol-based solution is probably better, then, short of defining your own macro,

To be honest, I'm trying to avoid macros as much as possible in our codebase. I understand why TCA is using them, but in general, the macro system in Swift brings more problems than benefits at this point. Hopefully, it will be fixed in the future. I have one warning and around 80 places where I need to do a workaround with protocols and different files. I'll wait. Maybe TCA tools will come up with some smart ideas later on.

[lukeredpath]

@3a4oT I understand your concerns about macros but honestly, I think TCA is at a point now where trying to use it without macros is very very difficult, if not impossible. You can avoid certain conveniences like the @Reducer and @DependencyClient macros but so much stuff is driven by case key paths that trying to avoid @CasePathable is just going to result in a huge amount of manual code you'll need to implement.

[3a4oT]

I'll rephrase. I'm OK with using macros from vendors like TCA (they're actively maintained and have good support). just don't want to maintain it internally and dance around swift-syntax versions or other things.

[stephencelis]

@3a4oT Did the second option work? It requires an extra line for the conformance but I think I had it building locally.

In general we are open to ideas on how to better support generic case key paths (i.e. protocols that declare a particular case key path in a conformance), but we're not sure how to make it simpler than the above right now.

Maybe an enhancement to @CasePathable or another macro in the library would help, but we're not sure what it would look like.

[3a4oT]

extension SomeReducer.Action.AllCasePaths: HasAnalyticsEventCasePath {}

Unfortunately, it doesn't work either. I get a compilation error: Type 'SomeReducer.Action.AllCasePaths' does not conform to protocol 'HasAnalyticsEventCasePath'

I was trying on Xcode 16 beta 4