Use RAC to detect first drag after the map is loaded

MapDidDrag_RAC.swift

import ReactiveSwift
import Result

class MapViewController: UIViewController {
  
    private let (didLoadSingal, didLoadObserver) = Signal<Bool, NoError>.pipe()
    private let (didDragSignal, didDragObserver) = Signal<Bool, NoError>.pipe()
  
    override func viewDidLoad() {
        super.viewDidLoad()
  
        let (signal, observer) = Signal<Signal<Bool, NoError>, NoError>.pipe()
        signal.flatten(.concat).take(first: 1).observeCompleted { [unowned self] in self.mapDidDrag() } 
      
        observer.send(value: loadedSingal)
        observer.send(value: didDragSignal)
        observer.sendCompleted() 
    }    
}

extension MapViewController: MKMapViewDelegate {
    func mapViewDidChangeVisibleRegion(_ mapView: MKMapView) {
        didDragObserver.sendCompleted()
    }

    func mapViewDidFinishLoadingMap(_ mapView: MKMapView) {
        loadedObserver.sendCompleted()
    }
}