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.