Cay S. Horstmann - Scala for the Impatient, 3rd Edition

The evolution of traditional languages has slowed down considerably, and programmers who are eager to use more modern language features are looking elsewhere. Scala is an attractive choice; in fact, I think it is by far the most attractive choice for programmers who want to improve their productivity. Scala has a concise syntax that is refreshing after the Java boilerplate. It runs on the Java virtual machine (JVM), providing access to a huge set of libraries and tools. And Scala doesnt just target the JVM. The ScalaJS project emits JavaScript code, enabling you to write both the server-side and client-side parts of a web application in a language that isnt JavaScript. Scala embraces the functional programming style without abandoning object orientation, giving you an incremental learning path to a new paradigm. The Scala REPL lets you run quick experiments, which makes learning Scala very enjoyable. Last but not least, Scala is statically typed, enabling the compiler to find errors, so that you dont waste time finding themor notlater in the running program. The compiler also helps you write error-free code, inferring types whenever possible so that you dont have to write (or read) them.

The first edition of this book was written when Java, C#, and C++ were mired in a malaise of ever-increasing complexity with little gain in expressive power. At the time, Scala was a welcome blast of fresh air. In the meantime, Java and other JVM languages such as Kotlin have embraced parts of the feature set of Scala. However, Scala has been blazing new trails in type-level programming, which make powerful libraries possible that you could simply not envision in a language such as Java or Kotlin.

I wrote this book for impatient readers who want to start programming in Scala right away. I assume you know Java, C#, JavaScript, Python, or C++, and I dont bore you with explaining variables, loops, or classes. I dont exhaustively list all the features of the language, I dont lecture you about the superiority of one paradigm over another, and I dont make you suffer through long and contrived examples. Instead, you will get the information that you need in compact chunks that you can read and review as needed.

Scala has gained a reputation for being difficult to read, and this can certainly be true when library providers pay little attention to usability or assume that programmers are fluent in category theory. I assume that you are comfortable with object-oriented programming. I cover what you need for basic functional programming, similar in complexity to Java streams, but there are no monads to be seen. My goal is to teach you to write Scala code that is delightful rather than inscrutable.

Scala is a big language, but you can use it effectively without knowing all of its details intimately. Martin Odersky, the creator of Scala, has identified levels of expertise for application programmers and library designersas shown in the following table.

For each chapter (and occasionally for individual sections), I indicate the experience level required. The chapters progress through levels A1, L1, A2, L2, A3, L3. Even if you dont want to design your own libraries, knowing about the tools that Scala provides for library designers can make you a more effective library user.

This is the third edition of this book, and I updated it thoroughly for Scala 3. Scala 3 brings major changes to the language. Classic features have been made more regular by removing awkward corner cases. Advanced features are now easier to learn. Even more powerful features have been added that were previously only available via macros. A quiet syntax, similar to that of Python, is easy on the eyes and is now the preferred way to write Scala 3 code.

I cover Scala 3 as it is and will be, and do not get into an elaborate evolutionary history of the past. If you need to work with Scala 2, get the second edition of this book.

I hope you enjoy learning Scala with this book. If you find errors or have suggestions for improvement, please visit http://horstmann.com/scala and leave a comment. On that page, you will also find up-to-date installation instructions, and an archive file containing all code examples from the book as executable programs or worksheets.