if you'd like to try out some of the new features coming in Swift 4, I made a playground to do just that. I thought I'd tell the list about it because some of you may find it useful.
You can download the playground on GitHub: https://github.com/ole/whats-new-in-swift-4
The playground requires Swift 4 (duh!). You need to install the latest Swift 4.0 snapshot from https://swift.org/download/#snapshots and, after installing it, select the toolchain in Xcode.
I plan to keep the playground updated over the summer as more features get implemented.