objc.io Issue #16 is all about Swift programming language. One of the most interesting articles is focused on rapid prototyping using Playgrounds.
Many developers enjoy building OS X or iOS applications because of how quickly one can create a viable application using the Cocoa frameworks. Even complex applications can be designed and built by small teams, in large part because of the capabilities provided by the tools and frameworks on these platforms. Swift playgrounds build on this tradition of rapid development, and they have the potential to change the way that we design and write OS X and iOS applications.