Add support for string arrays to AppStorageKey

[ph1ps]

Kind of a weird exception, but UserDefaults supports [String] natively, so I'd suggest to also add support to AppStorageKey. Theoretically, users could create their own workarounds here, by just serializing/deserializing the array and using Data as an intermediate, so this addition might not be necessary.

Alternatively, I could take a look to support arrays in general: https://developer.apple.com/documentation/foundation/userdefaults/1414792-array. However, this might add a lot of overloads.

What do you think?

[stephencelis]

@ph1ps We've resisted expanding the surface area here to keep things in line with Apple's @AppStorage, which omits this ability, as well as the ability to use Codable.

We're open to revisiting this, but would want to do so in a holistic manner that also considers support for Codable, especially since [String] is technically Codable. We can leave this PR open for now as a reminder, but we might not get back to it right away.

[winnisx7]

Thanks for the great library!

I've noticed that @shared(.fileStorage) already supports Codable through optional encoder and decoder parameters. However, @shared(.appStorage) doesn't currently support Codable types in a similar way, despite having a very similar API design.

Could you share the reasoning behind why fileStorage supports custom encoder and decoder, but appStorage does not? Would it make sense to align appStorage with the existing fileStorage design to provide consistent support for Codable types?

@stephencelis

[winnisx7]

Currently, I'm forced into a quite unfortunate workaround:

@Shared(.appStorage("credential", store: .standard))
private var credentialData: Data?

var credential: OAuthCredential? {
  set {
    $credentialData.withLock { credentialData in
      if let newValue = newValue {
        credentialData = try? JSONEncoder().encode(newValue)
      } else {
        credentialData = nil
      }
    }
  }
  get {
    $credentialData.withLock { credentialData in
      if let credentialData = credentialData {
        return try? JSONDecoder().decode(OAuthCredential.self, from: credentialData)
      } else {
        return nil
      }
    }
  }
}

It would be great if @shared(.appStorage) could follow the same pattern as fileStorage, allowing for clean and direct Codable support, thus avoiding such painful boilerplate.

[ph1ps]

I think this should be moved to a discussion, rather than commenting on this MR.

[stephencelis]

@winnisx7 We are not opposed to exploring what it means to add support for codable, but it certainly isn't straightforward, and the fact that Apple omits support in @AppStorage is telling. This has been talked about in other PRs and discussions, so I'll direct you to a recent one: #48