Interesting that Apple released iOS 8.3 beta today when iOS 8.2 beta isn't even on GM yet.
Anyhow, iOS 8.3 amd Xcode 6.3 (with Swift 1.2) are available for download right now in a beta capacity. If you want to play around with these new versions, head to Apple Developer Center and download them.
On the official Swift Blog, Apple announced that Swift has a bunch of new features at the language level, atop of several improvements on the compiler side of things (Xcode 6.3 now supports incremental builds for Swift. Yay!).
One of the most notable additions to Swift in its 1.2 revision is the new native type,
Set, that maps directly to its Objective-C counterpart,