This book was about, well, the Swift Programming Language. It explained how to use Swift, from printing "hello world", to building full applications for iOS, MacOS, WatchOS, and tvOS. It explains conditionals, functions, error catching, property and class inheritance and mutations, and much much more. My favorite part of the book was generic class functions, because it is a very smart implementation of Swift that allows for writing clean, effective code. I would recommend this book to people who want to develop for the Apple API, which includes all major Apple software platforms. Just know, that this book is 1300 pages long, and will make you want to cry every time you read it.