Accessing an element in a shared collection.

[hayek]

Given a shared collection such as an Array, the only way to access it's elements by using a subscript is by casting:

@Shared(.favorites) var favorites
return favorites[0] // compilation error: Setter for 'favorites' is unavailable: Use '$shared.withLock' to modify a shared value with exclusive access.
return (favorites as Array<String>)[0] // compiles

Having an extension to wrap the subscript in a function also works:

extension Array {
    func value(at index: Int) -> Element {
        return self[index]
    }
}
...
@Shared(.favorites) var favorites
return favorites(at: 0)

The reason behind this error is that the Sharing framework utilizes dynamic member lookup's subscript to surface the value of the wrapped reference.

Is there any solution in swift to enable both dynamic member lookup and subscripts of types to work without the workarounds I mentioned?

[mbrandonw]

Hi @hayek, the error you are seeing should only happen when setting the value. Not when merely accessing the value. This code compiles just fine for me:

func foo() -> Int {
  @Shared(.inMemory("favorites")) var favorites = [42]
  return favorites[0]
}

Can you share some code that produces a compilation error from only accessing the state?

[hayek]

Well it seems to be an Xcode version related. The code you posted compiles under Xcode 16.2 but under 15.2 I get the error.

[mbrandonw]

Hi @hayek, that does seem to be a bug in older Swift versions. I just opened this PR #64 that should help.