Looks like plans for Swift 4 are firming up and various manifesto documents (for example, Strings last week) are making their way into the Swift repository. This one is a very thorough discussion of ABI stability.
Ole Begemann talks customisation of string interpolation in Swift. He defines two new string types to hold sanitised and unsanitised HTML strings that behave differently when interpolated. There's some code in here which is already deprecated awaiting a redesign in 4, but it's still a really interesting post.
Erica Sadun with far too many ways to get that optional populated! 😀 You might also find Russ Bishop's extensions to Optional interesting if you like this.
Yes, this article is actually about Android apps, but it's a great reminder to double check your code for this kind of problem.