Migrate NSUserDefaults to App Groups - Swift

MigrateDefaults.swift

func migrateUserDefaultsToAppGroups() {
	
	// User Defaults - Old
	let userDefaults = NSUserDefaults.standardUserDefaults()
	
	// App Groups Default - New
	let groupDefaults = NSUserDefaults(suiteName: "group.myGroup")
	
	// Key to track if we migrated
	let didMigrateToAppGroups = "DidMigrateToAppGroups"
	
	if let groupDefaults = groupDefaults {
		if !groupDefaults.boolForKey(didMigrateToAppGroups) {
			for key in userDefaults.dictionaryRepresentation().keys {
				groupDefaults.setObject(userDefaults.dictionaryRepresentation()[key], forKey: key)
			}
			groupDefaults.setBool(true, forKey: didMigrateToAppGroups)
			groupDefaults.synchronize()
			print("Successfully migrated defaults")
		} else {
			print("No need to migrate defaults")
		}
	} else {
		print("Unable to create NSUserDefaults with given app group")
	}
	
}

An updated version of your code to Swift 4

func migrateUserDefaultsToAppGroups() {
        
        // User Defaults - Old
        let userDefaults = UserDefaults.standard
        
        // App Groups Default - New
        let groupDefaults = UserDefaults(suiteName: "group.myGroup")
        
        // Key to track if we migrated
        let didMigrateToAppGroups = "DidMigrateToAppGroups"
        
        if let groupDefaults = groupDefaults {
            if !groupDefaults.bool(forKey: didMigrateToAppGroups) {
                for key in userDefaults.dictionaryRepresentation().keys {
                    groupDefaults.set(userDefaults.dictionaryRepresentation()[key], forKey: key)
                }
                groupDefaults.set(true, forKey: didMigrateToAppGroups)
                groupDefaults.synchronize()
                print("Successfully migrated defaults")
            } else {
                print("No need to migrate defaults")
            }
        } else {
            print("Unable to create NSUserDefaults with given app group")
        }
        
    }