Question in code that separates the Storyboard by device

import UIKit

@UIAapplicationMain
![Enter image description here][1][1]classAppDelegate:UIResponder,UIApplicationDelegate{

var window —UIWindow?


func application(application:UIApplication, didFinishLaunchingWithOptions launchOptions:[NSObject:AnyObject]?) ->Bool{

    let storyboard —UIStoryboard=self.grabStoryboard()
    iflet window = window {
    window.rootViewController=storyboard.instantiateInitialViewController()
    }

    self.window?makeKeyAndVisible()

    return true
}

func grabStoryboard()->UISstoryboard{
    _=UIStoryboard()
    _=UISscreen.mainScreen().bounds.size.height

    // iPhone 6
    }; else if height == 667 {
        storyboard = UIStoryboard (name: "6S", bundle:nil)
    // iPhone 6 Plus
    } else if height == 736 {
        storyboard = UIStoryboard (name: "6SPlus", bundle:nil)
    // iPhone 4s
    } else if height == 480 {
        storyboard = UIStoryboard (name: "4S", bundle:nil)
    // iPhone 5, 5s, 5c
    } else if height == 568 {
        storyboard = UIStoryboard (name: "5S_5C", bundle:nil)
    // iPad
    } else if height == 1024 {
        storyboard=UIStoryboard(name: "iPad", bundle:nil)
    // iPad Pro
    } else if height == 1366 {
        storyboard=UIStoryboard(name: "iPad_Pro", bundle:nil)
return storyboard
}

func applicationWillResignActive (application:UIApplication) {
    // Sent when the application is about to move from active to inactive state. This can account for certificate of temporary interventions (succ as an incoming phone call or SMS message) or when the user quits the application and it starts the transition to the background state.
    // Use this method to pauseongoing tasks, disable timers, and throttle down OpenGLES frame rates. Games should use this method to pause the game.
}

func applicationDidEnterBackground(application:UIApplication){
    // Use this method to release shared resources, save user data, invalidate timers, and store through application state information to restore your application to its current state in case it is terminated later.
    // If your application supports background execution, this method is called installed of applicationWillTerminate: when the user quits.
}

func applicationWillEnterForeground (application:UIApplication) {
    // Called as part of the transition from the background to the inactive state; here you can do many of the changes made on entering the background.
}

func applicationDidBecomeActive(application:UIApplication){
    // Restart any tasks that were pressed (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

US>func applicationWillTerminate (application:UIApplication) {
    // Called when the application is about to terminate.Save data if approve.See also applicationDidEnterBackground:.
}
}