In spite of Apple expressing a desire to switch its apps to Swift, just a handful of them are actually using the programming language so far, according to a software engineer.
The Calculator app is the only part of iOS 9.2 that includes any Swift code, Ryan Olson noted in a blog post. It is at least said to be nearly "pure" Swift, with only two of 22 classes written in Apple's previous favorite language, Objective-C.
Even Apple apps that are optional downloads from the App Store are generally reliant on Objective-C, Olson added. The official WWDC app makes use of some Swift, as does the Apple Store app's Watch interface, but even the former only contains Swift in six out of 281 classes.
The problem likely stems from several issues, such as the Swift Application Binary Interface not being finished. This should happen by Swift 3, but until then app compatibility may be too prone to breaking. There's also no 32-bit Swift runtime for OS X.
In December Apple's senior VP of Software Engineering, Craig Federighi, said that El Capitan's Dock and window management code was done with Swift, and that the iCloud team is "champing at the bit" to try the language. Deeper integration may have to wait until newer iOS and OS X releases later this year.