I have a simple Microphone class which conforms to @Observable, with public properties that trigger redraws for some SwiftUI Views. But I also want these property changes to trigger logic in non-Views, e.g. to start or stop speech recognition.

@Observable public class Microphone: NSObject {

    public enum State: String {
        case muted
        case off
        case on
        case starting
    }

    public var state: State = .off
}

Before the introduction of @Observable in iOS 17, the Microphone would implement ObservableObject, and its properties would be @Published, so non-Views could call sink() on them to get updates. But now there doesn't seem to be a way to do this.

I tried adding @Published to the state property declaration, but there are two compiler errors:

>

.../Microphone.swift Cannot convert value of type 'ReferenceWritableKeyPath<Microphone, Published<Microphone.State>>' to expected argument type 'ReferenceWritableKeyPath<Microphone, Microphone.State>'

/var/folders/zl/9mrxbhjd0kxfj1763408zfh80000gq/T/swift-generated-sources/@_swiftmacro_10CDAFMobile10MicrophoneC5state18ObservationTrackedfMp.swift:1:46 Invalid redeclaration of synthesized property '_state'

The synthesized code hints that maybe I can declare the state property as both @Published and @ObservationIgnored. Now it compiles, but it's unclear whether this will still cause Views to be refreshed. Is there a better way to handle this?