Advanced Swift. Chris Eidhof, Ole Begemann, Airspeed Velocity

If you have read the Swift Programming Guide, and want to explore more, this book is for you
Swift is a great language for systems programming, but also lends itself for very high-level programming. We’ll explore both high-level topics (for example, programming with generics and protocols), as well as low-level topics (for example, wrapping a C library and string internals)