After spending a weekend playing with Swift I encountered a few surprises.

Categories & Extensions

Categories are one of my favorite features of Objective-C. I can modify the behavior of any class.

Swift doesn’t have categories. Instead it has extensions. I was immediately surprised to find extensions are available throughout the entire app target (whereas categories are only available if and where you include them.)

Compatibility

Ever since the announcement I wondered how Apple is able to support past devices. After all, iOS7 and OS X 10.9 were released with pre-Swift runtimes. Turns out Swift apps embed the Swift runtime in each app bundle, which is how they are able to run consistently and predictably on past, present, and future devices, even while the language is experiencing the churn of a beta release.

Which brings me to the next point…

Expect Change

We’ve already seen a lot of changes and tweaks to the language since it’s announcement.

And Apple expects Swift to change alot over the next two years.

It would be dangerous to rely upon binary frameworks that use Swift — especially from third parties. As Swift changes, those frameworks will be incompatible with the rest of your app. When the binary interface stabilizes in a year or two, the Swift runtime will become part of the host OS and this limitation will no longer exist.

Privacy

For seven releases of iOS we’ve never had private access control in our classes. As of XCode 6 beta 4 that changes — we now have truly private access control. This is certainly a new and welcome addition to the world of iOS development!