LocationManager with PromiseKit-Swift. Well I don't like this deferred at all.

LocationManager.swift

import Foundation
import CoreLocation


class LocationManager : NSObject, CLLocationManagerDelegate {
    
    class var sharedInstance : LocationManager {
        get {
            struct Static {
                static let instance : LocationManager = LocationManager()
            }
            return Static.instance
        }
    }
    
    let locationManager:CLLocationManager = CLLocationManager()
    var requestAuthorizationDeffered:(Promise<Bool>, (Bool)->(Void), (NSError)->(Void))? = nil
    
    var isAvailable:Bool {
        get {
            if !CLLocationManager.locationServicesEnabled() {
                return false
            }
            switch CLLocationManager.authorizationStatus() {
                case .Authorized, .AuthorizedWhenInUse: return true
                default: return false
            }
        }
    }
    
    init() {
        super.init()
        self.locationManager.delegate = self;
    }
    
    func requestAuthorization() -> Promise<Bool> {
        if let deffered = self.requestAuthorizationDeffered {
            return deffered.0
        }
        
        self.locationManager.requestWhenInUseAuthorization()
        let deffered = Promise<Bool>.defer()
        self.requestAuthorizationDeffered = deffered
        return deffered.0
    }
    
    // MARK: - CLLocationManagerDelegate
    
    func locationManager(manager: CLLocationManager!, didChangeAuthorizationStatus status: CLAuthorizationStatus) {
        if let deffered = self.requestAuthorizationDeffered {
            deffered.1(self.isAvailable)
            self.requestAuthorizationDeffered = nil
        }
    }
}