@Shared behavior in Xcode previews appears to have changed with Xcode 26

[kevinanderson7]

In Xcode 26 beta 1 and beta 2, I have noticed unusual behavior when using the Shared property wrapper in Xcode previews. Before the Xcode 26 beta, it was easy to configure multiple previews in a given file to use different Shared values so that each preview could be spun up in a very specific state. For Xcode 26 beta 1 and 2, I have noticed that while this once worked great in previous Xcode versions, it no longer seems to produce the correct result.
I have provided a link to a repro here: https://github.com/kevinanderson7/swift-sharing/tree/xcode-previews-repro.

If I build the Xcode previews with Xcode 26 beta 1 or 2, the Shared value declared in the first preview of the file is the only one used across the 2 other previews. However if I build the Xcode previews using Xcode 16.4, each preview is spun up with the proper Shared value. Any idea why this might be?

[ZevEisenberg]

I am seeing the same issue in Xcode 26 beta 2. Previews appear to be, well, sharing a single shared value. I'm using an in-memory key defined like this:

extension SharedKey where Self == InMemoryKey<Bool>.Default {
  static var isRecording: Self {
    Self[.inMemory("isRecording"), default: false]
  }
}

I'm actually not sure what the recommended way is to populate shared values in previews. I've tried this:

@Previewable @Shared(.isRecording) var isRecording = false

And this:

#Preview {
  @Previewable @Shared(.isRecording) var isRecording

  MyView()
    .onAppear { $isRecording.withLock { $0 = false }
}

But I'm not sure which, if either, is preferred.