This was one of the better books I’ve read recently for actually changing how I think about programming. It combines domain-driven design, test-first development, and functional programming into one coherent story, which is pretty rare, since most books only tackle one of those at a time. Unlike some of my other recent reads, the Kotlin itself was well-structured and idiomatic throughout, not just functional-flavored Java. ...
Better than initially assessed: Chapter 2 introduces collections, good variance coverage (with a Pet hierarchy), covers extensions and their role in the stdlib, two lambda/HOF chapters. Unusual ordering: generics before lambdas. map/filter/fold deferred to lambda chapters. Coroutines appendix exists but dated. Head First Kotlin uses the usual Head First spiral approach - introduce a concept lightly, let it sit, circle back with depth later - which meant it deferred anything not strictly load-bearing to the appendices. Labeled breaks and enum classes, both things I’d consider core language features, got pushed all the way to Appendix C rather than covered in the main chapters. That appendix is even honest about it in the title: “The Top Ten Things (We Didn’t Cover)” - ten separate topics, including packages, visibility modifiers, sealed classes, and object declarations, that never made it into the twelve main chapters at all. ...
Kotlin from Scratch is a project book, and the projects are mostly math and computation: Euclid’s algorithm, the Sieve of Eratosthenes, Fibonacci, physics simulations, fractals, sorting, and A* search. It was good typing practice, and some of the math and algorithms were really interesting, but it was disappointing as a source of good Kotlin code. The first two chapters covered the language fundamentals in almost as much depth as all of Head First Kotlin, but that depth never came back. Nothing after chapter 2 touches generics, sealed classes, delegation, or coroutines, extension functions never show up, and the language features stay limited. Chapter 3 was a whole detour into JavaFX that I didn’t ask for and won’t need for Android or Swift, though I don’t regret typing it, since the Stage and Scene boilerplate turned into a really cool spiral, and fighting the Gradle multi-module setup taught me more about the build system than the book itself did. ...