How iOS 9 will make the file size of your games smaller

Something that Apple only briefly mentioned during the WWDC the other day was a feature of iOS 9 called "app thinning."

It's exactly as it sounds: developers can use it to make the file size of apps smaller. This means that with iOS 9 you should hopefully have more free space.

Ars Technica has been going through the iOS 9 developer documentation and has discovered that there are three methods by which developers can utilize app thinning.

The first is called App Slicing. It eliminates any of the bits of code in an app that your iPhone or iPad doesn't need.

Previously, when you downloaded an app, it would grab all the code necessary to make it run on all iOS devices. If you have an iPhone 5, right now your apps have the code required for them to run on an iPhone 6.

Your iPhone 5 doesn't need this iPhone 6 code, though. And so App Slicing will ensure you don't download code such as that in the future.

Secondly is On-Demand Resources (ODRs). With this, an app will only download assets that it reasons you'll require immediately or in the near future. And once you're done with assets it will delete them.

If you've played a tutorial of a game, and the app determines you won't need to play it again, with ODRs it will delete the tutorial's assets to save space.

Note that ODRs doesn't delete executable code so it can't accidentally delete an entire game while you're playing it. But it will get rid of elements like images and media files.

However, it's not clear if ODRs will affect your playing experience if, say, you're offline. How will an app without all the necessary assets download them if it can't get online? Will that mean some of the game is unavailable? It seems likely.

The third app thinning method is called "Bitcode." With this, when developers upload an app to the App Store only an "intermediate representation" of it is stored. The rest is compiled on demand.

Bitcode informs some of the App Slicing feature as it determines whether you'll download a 32-bit or 64-bit file.