“Of all the new features introduced in iOS 8 last week, app extensions are the ones that will have the biggest, most visible impact on the new operating system,” Andrew Cunningham reports for Ars Technica. “The feature is most commonly described as a way for third-party applications to talk to each other, though that’s an oversimplification—that’s not the only thing app extensions can do, and technically third-party apps in iOS still can’t talk directly to one another.”

“Allowing third-party apps to communicate with other apps is just one of the problems extensions are meant to solve — third-party keyboards, connecting apps to cloud services other than iCloud, and the new Notification Center widgets are all their own kind of extensions,” Cunningham reports. “Not all parts of iOS can be changed (or ‘extended’) by third parties. If you wanted to replace one of the default apps with your own or add some kind of toggle to the Control Center, you can’t do that. Apple defines a handful of pre-set ‘extension points’ to show developers where they can add stuff.”

“A simple way to summarize all of this: Apple doesn’t want one app to be able to get into another app’s sandbox,” Cunningham reports. “Extensions are like little sandboxes-within-sandboxes that facilitate communication between different apps while never sharing all of their containing app’s data directly with the host app.”

Much more in the full article here.