These annotations already exist and developers already use them. As stated in the article you have to use the @2x naming convention to label double resolution images. Similarly you have to use the ~iPhone and ~iPad naming conventions for xibs and any other resource that's different on iPhone and iPad.

When making a universal app you are already forced to do this. Take a look at the Twitter app: it is completely different on iPad vs iPhone. These labels are how it knows what interface to load on each device -- yet the code and resources to load either exist regardless of what device you are on.

There's a png in the project. Is it an icon that's used by both iPhone and iPad? A background image used by only one? A texture they share? The nib and @2x annotations don't handle that stuff.

Yes they do: If its an image that gets used in both situations then you don't annotate it. In fact thats the common case. You only annotate the few resources and classes that are different on each platform. It's not complex, and it's also not a system I've invented, it's the system developers are already forced to use by Apple: http://developer.apple.com/library/ios/ipad/#documentation/2... (scroll to "updating your image resource files", you'll see it handles all the cases you mentioned, and the same applies to xibs)

And it works fine except for the fact that it chooses the resource at runtime. When you ask for resource "x" it looks for all the resources that start with "x" but may end with @2x or ~iPhone or whatever. It then decides which to return based on what device you have. There is no reason it cant make this determination at compile-time and just not include the resources it knows it won't be using in four separate builds. There is literally no difference with this system except when it chooses to ignore resources.

Oh. I didn't realize you could apply a device modifier to an image. Thanks.