Improve ergonomics of SwitchStore with no action

[AndreiVidrasco]

Describe the bug
Hi. Is it possible to somehow ergonomics when SwitchStore doesn't need any actions?
See example below. Basically, I want to have a way to get rid of all this action closure.
At the moment it doesn't compile, if I remove.

struct ContentViewState: Equatable {
    let viewTypes: DifferentViewTypes
}

enum DifferentViewTypes: Equatable {
    case noData
    case genericError
    case serverResponse(String)
}

struct ContentView: View {
    var store: Store<ContentViewState, Never>
    
    var body: some View {
        SwitchStore(store.scope(state: \.viewTypes, action: { i in fatalError() })) {
            CaseLet(state: /DifferentViewTypes.genericError, action: { _ in }, then: GenericErrorView.init)
            CaseLet(state: /DifferentViewTypes.noData, action: { _ in }, then: NoDataView.init)
            CaseLet(state: /DifferentViewTypes.serverResponse, action: { _ in }, then: ServerResponseView.init)
        }
    }
}

struct NoDataView: View {
    var store: Store<(), Never>
    
    var body: some View {
        Text("No Data")
    }
}

struct GenericErrorView: View {
    var store: Store<(), Never>
    
    var body: some View {
        Text("Generic Error")
    }
}


struct ServerResponseView: View {
    var store: Store<String, Never>
    
    var body: some View {
        WithViewStore(store) { viewStore in
            Text(viewStore.capitalized)
        }
    }
}

Expected behavior
Have a way to not include actions conversion in case of never

[mbrandonw]

I am going to convert this to a discussion as it is not an issue with the library.

[mbrandonw]

You can perform self.store.actionless to turn any store into one that has Never for its actions:

swift-composable-architecture/Sources/ComposableArchitecture/Store.swift

Line 407 in e7dda73

public var actionless: Store<State, Never> {

Also, the action argument of .scope is optional, so you can leave that off once you apply .actionless.

[iampatbrown]

This seems to work for me.

public extension CaseLet where GlobalAction == Never, LocalAction == Never {
  init(
    state toLocalState: @escaping (GlobalState) -> LocalState?,
    @ViewBuilder then content: @escaping (Store<LocalState, LocalAction>) -> Content
  ) {
    func absurd<A>(_ never: Never) -> A {}
    self.init(state: toLocalState, action: absurd, then: content)
  }
}

struct ContentView: View {
  var store: Store<ContentViewState, Never>

      var body: some View {
        SwitchStore(store.scope(state: \.viewTypes)) {
              CaseLet(state: /DifferentViewTypes.genericError, then: GenericErrorView.init)
              CaseLet(state: /DifferentViewTypes.noData, then: NoDataView.init)
              CaseLet(state: /DifferentViewTypes.serverResponse, then: ServerResponseView.init)
          }
      }
}

[AndreiVidrasco]

ok, that looks like it. is it possible to add in the main library?
also just a suggestion, maybe to add also this extension

extension CaseLet {
    public init(
      state toLocalState: @escaping (GlobalState) -> LocalState?,
      @ViewBuilder then content: @escaping () -> Content
    ) where LocalAction == Never, GlobalAction == Never, LocalState == Void {
        func absurd<A>(_ never: Never) -> A {}
        self.init(state: toLocalState, action: absurd, then: { _ in content() })
    }
}

in case there is no action and no state, we can remove store from content block.
then I can remove var store: Store<(), Never> inside the View and also keep the nice syntax of then: GenericErrorView.init)

[mbrandonw]

Sorry about that! Sent my comment from my phone and so I didn't catch the nuances of the problem. Y'all are both right that an overload of CaseLet.init is needed, so we'll discuss adding that to the library today!

[iampatbrown]

Sounds good :)

[mbrandonw]

After discussing we decided to not add this overload. Extra overloads come with autocomplete fatigue, and this one in particular seems to only service a very small set of situations. We have other overloads in the library that we'd also like to get rid of, and may soon start deprecating them.

FWIW, you can slightly shorten your code to this:

SwitchStore(store.scope(state: \.viewTypes)) {
  CaseLet(state: /DifferentViewTypes.genericError, action: { _ in }, then: GenericErrorView.init)
  CaseLet(state: /DifferentViewTypes.noData, action: { _ in }, then: NoDataView.init)
  CaseLet(state: /DifferentViewTypes.serverResponse, action: { _ in }, then: ServerResponseView.init)
}

And you can shorten more if you bring in the convenience initializer into your own code base.