I've create a small

ObservableStore

class like this:

class ObservableStore<T>(state: T) : ObservableState<T> {
    private val observers = mutableListOf<(T) -> Unit>()

    var state: T by Delegates.observable(state) { _, _, new ->
        observers.forEach { it(new) }
    }

    override fun getState(): T {
        return state
    }

    override fun subscribe(observer: (T) -> Unit): () -> Unit {
        observers += observer
        observer(state)
        return {
            observers -= observer
        }
    }
}