Rx\Observable::just PHP Method

    public static function just($value)
    {
        return new ReturnObservable($value);
    }

 /**
  * @inheritDoc
  */
 public function __invoke(ObservableInterface $observable, ObserverInterface $observer, SchedulerInterface $scheduler = null)
 {
     if ($this->scheduler !== null) {
         $scheduler = $this->scheduler;
     }
     $innerDisp = new SerialDisposable();
     $disp = $observable->subscribe(new CallbackObserver(function ($x) use($innerDisp, $observer, $scheduler) {
         $now = $scheduler->now();
         if ($this->nextSend <= $now) {
             $innerDisp->setDisposable(new EmptyDisposable());
             $observer->onNext($x);
             $this->nextSend = $now + $this->throttleTime - 1;
             return;
         }
         $newDisp = Observable::just($x)->delay($this->nextSend - $now)->subscribe(new CallbackObserver(function ($x) use($observer, $scheduler) {
             $observer->onNext($x);
             $this->nextSend = $scheduler->now() + $this->throttleTime - 1;
             if ($this->completed) {
                 $observer->onCompleted();
             }
         }, [$observer, 'onError']), $scheduler);
         $innerDisp->setDisposable($newDisp);
     }, function (\Exception $e) use($observer, $innerDisp) {
         $innerDisp->dispose();
         $observer->onError($e);
     }, function () use($observer) {
         $this->completed = true;
         if ($this->nextSend === 0) {
             $observer->onCompleted();
         }
     }), $scheduler);
     return new CompositeDisposable([$disp, $innerDisp]);
 }