SwitchStore in Preview results in multiple screens

[gsl-anthonymerle]

Description

Hi!

So I was working with the SwitchStore and wanted to showcase various cases using the XCode's Live Preview feature
There are no crash or important bug per se, but in the Preview's Canvas, I see N variations for each use case I have in the preview. With N being the number of cases in my enum State

I tried with a Vanilla SwiftUI switch statement in my View, but the behaviour was, as expected, to see only three previews in the canvas

I believe that this behaviour is a direct result of CaseLet view using the IfLetStore under the hood, which results in multiple if-else statements in place of a switch statement

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Seeing only 3 preview contents (3 because I have explicitly added 3 previews to my preview provider)

Actual behavior

I see N preview contents (N being 3 times the number CaseLet/Default views I have in my SwitchStore)

Steps to reproduce

Using the following sample, just check the XCode's live preview:

import ComposableArchitecture
import SwiftUI

struct TestReducer: ReducerProtocol {
    enum State: Equatable {
        case content(String)
        case other(String)
        case nothing
    }

    enum Action: Equatable {}

    var body: some ReducerProtocolOf<Self> {
        EmptyReducer()
    }
}

struct TestView: View {
    let store: StoreOf<TestReducer>

    var body: some View {
        SwitchStore(store) { _ in
            CaseLet(
                state: /TestReducer.State.content,
                action: { (action: TestReducer.Action) in action }
            ) { store in
                Text("Content")
            }

            CaseLet(
                state: /TestReducer.State.other,
                action: { (action: TestReducer.Action) in action }
            ) { store in
                Text("Other")
            }

            CaseLet(
                state: /TestReducer.State.nothing,
                action: { (action: TestReducer.Action) in action }
            ) { store in
                Text("Nothing")
            }
        }
    }
}

struct TestView_Previews: PreviewProvider {
    static var previews: some View {
        TestView(store: .init(
            initialState: .content("Hello, world!"),
            reducer: TestReducer()
        ))
        .previewDisplayName("Content")

        TestView(store: .init(
            initialState: .other("Hello, other world!"),
            reducer: TestReducer()
        ))
        .previewDisplayName("Other")

        TestView(store: .init(
            initialState: .nothing,
            reducer: TestReducer()
        ))
        .previewDisplayName("Loading")
    }
}

The Composable Architecture version information

0.54.0

Destination operating system

iOS 15 and later

Xcode version information

Version 14.3.1 (14E300c)

Swift Compiler version information

swift-driver version: 1.75.2 Apple Swift version 5.8.1 (swiftlang-5.8.0.124.5 clang-1403.0.22.11.100)
Target: arm64-apple-macosx13.0

[stephencelis]

SwitchStore expects you to explicitly switch over the initial state that is passed along:

-SwitchStore(store) { _ in
+SwitchStore(store) {
+  switch $0 {
+  case .content:
     CaseLet(
       state: /TestReducer.State.content,
       action: { (action: TestReducer.Action) in action }
     ) { store in
       Text("Content")
     }

+  case .other:
     CaseLet(
       state: /TestReducer.State.other,
       action: { (action: TestReducer.Action) in action }
     ) { store in
       Text("Other")
     }

+  case .nothing:
     CaseLet(
       state: /TestReducer.State.nothing,
       action: { (action: TestReducer.Action) in action }
     ) { store in
       Text("Nothing")
     }
+  }
 }

I believe this will get previews to work more as you expect.

Also note that CaseLet does not require the state: named argument. You can simply do:

CaseLet(/TestReducer.State.content, /* ... */)

Because this isn't a bug in the library I'm going to convert this to a discussion.

[gsl-anthonymerle]

Oh! 😳 So I was just using it wrong, my bad 🙏
Thank you for the explanation @stephencelis

Can I close the discussion, then ?