static void _processData(AppDelegate *self, NSInteger i) {

    // Notice that the _window can be accessed here, even though it is a private ivar

    // A compiler error (or warning) will happen if this method was outside the @implementation scope of AppDelegate.

    NSLog(@"Processing %d in window %@", i, self->_window);

}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {

    for (NSInteger i = 0; i < 200; i++) {

        _processData(self, i);

    }

}