Cleaning it up slightly

PickupFragment.kt

private typealias PageDebounceSelector = (data: PickupData) -> ObservableSource<Long>

class PickupFragment {

    override fun onStart() {
        super.onStart()
        source().viewStates()
            .debounce(loadingOnly)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe { data: PickupData ->
                adapter.setData(data)
            }
            .addTo(disposables)
    }

    private val loadingOnly: PageDebounceSelector =
        {
            when {
                it.isLoading() -> Observable.timer(250, TimeUnit.MILLISECONDS)
                else -> Observable.empty()
            }
        }
}