All 6 app delegate functions in swift 3 "nearly match optional requirement" - what is this? How to fix?

Question

Downloaded the xcode 8.2 beta last night, converted most of my code but am now stuck with yellow warning symbols regarding the six functions of the app delegate:

var window: UIWindow?


func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    // Override point for customization after application launch.
    return true
}

  func applicationWillResignActive(application: UIApplication) {
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES 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 enough 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 instead of applicationWillTerminate: when the user quits.
}

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

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

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

I am able to "fix" each function with either

  Rename to application(_:didFinishLaunchingWithOptions:)' to      satisfy this requirement

  Make 'application(application:didFinishLaunchingWithOptions:)'       private to slince this warning 

or

Add '@nonobjc' to silence this warning

considering I have not seen these three options before, would anyone mind explaining and any options to solve or disregard them?

Answer 1

This is all part of "renamification" and the Swift 3 change in the rules for the externalization of a method's first parameter.

So, do the first option: put in the _ to make _ application: (instead of application: plain and simple) as the name of the first parameter in every case. Otherwise, the application will be externalized and Objective-C will see these methods as being called applicationWithApplication... which is not what you want to have happen.

Don't do either of the others. You don't want to hide these methods from Objective-C (private or @nonobjc); you want Objective-C to see them, and in particular to see them as the app delegate protocol methods.