Why not assign MainWindowController to the let right away?

Cocoa Programming for OS X (5th Edition) 1. Let's Get Started
1

I know this question has a lot of Swift-related issues in it, and that will be covered later, but…

In the AppDelegate book example in Chapter 1 we seem to do a much of var/let dancing. I wonder considering the MainWindowController is going to be instantiated right away anyways if this might be a more lean implementation.

import Cocoa

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    let mainWindowController = MainWindowController(windowNibName: "MainWindowController")

    func applicationDidFinishLaunching(aNotification: NSNotification) {
        mainWindowController.showWindow(self)
    }
    
}

I suppose there is a risk the MainWindowController init might fail (maybe a typo in that string) but I’d consider that a compile time behavior not a run time behavior.

2

Good question. You’re right, it could be streamlined as shown, but we wanted to demonstrate a more flexible window controller pattern that allows for the window controller to not exist all the time. If this were a preferences window, for example, you probably wouldn’t want to have the PreferencesWindowController in memory except when it is visible. Thus the optional (var) property.

Does that help?

3

Awesome. Figured as much. Thanks for the info.