The Swift Programming Language - Apple Inc.

GoodReads Summary: Swift is a new programming language for creating iOS and OS X apps. Swift builds on the best of C and Objective-C, without the constraints of C compatibility. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more fun. Swift’s clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to reimagine how software development works.

Let's skip the language itself for a moment and focus on the writing of the book.

The interesting bit is the first 20-or-so pages. It starts with a very simple, very succinct explanation of the language, so if you any programming language, you can just start writing Swift code picking the pointers in those pages.

Then, the real content starts: It goes very deep, explaining every point in great detail, with expanding examples that start very simple at the start of the chapter and then go increasingly going complex to explain each point.

Really interesting way to explain a language.