const selectedViewsFromUrl: Observable<IView | null> = observableCombineLatest(routes, allViews.pipe(take(1)))
  .pipe(
    map(([route, views]) => {
      if (!views || views.length == 0) return null;
      const requestedView = route.relativePathSegments[1] || "";
      if (!requestedView) return null;
      const view = views.filter(v => v.name.toLowerCase() === requestedView.toLowerCase())[0];
      return view ? view : null;
    }),
    filter(v => v != null)
  );

// on first load, if no view is defined in the URL, check if there is only view and if so, select it
const automaticallySelectedSingleView: Observable<IView | null> = selectedViewsFromUrl
  .pipe(
    isEmpty(),
    filter(isEmpty => isEmpty === true),
    switchMap(() => allViews.pipe(
      take(1),
      filter(vs => vs != null && vs.length == 1),
      map(vs => vs == null ? null : vs[0])
    ))
  )
;

export const selectedViews: Observable<IView | null> = merge(
  selectedViewsFromUrl,
  automaticallySelectedSingleView
);

// fetching the data of a view

export function isEmpty<T>(this: Observable<T>): Observable<boolean> {
  return higherOrder()(this);
}

it('should infer correctly', () => {
  const o = of(1, 2, 3).pipe(isEmpty()); // $ExpectType Observable<boolean>
});

 observable1 = constructorZone1.run(() => {
   return of(1, 2, 3).pipe(isEmpty());
 });