Book Image

Learn Scala Programming

By : Slava Schmidt
Book Image

Learn Scala Programming

By: Slava Schmidt

Overview of this book

The second version of Scala has undergone multiple changes to support features and library implementations. Scala 2.13, with its main focus on modularizing the standard library and simplifying collections, brings with it a host of updates. Learn Scala Programming addresses both technical and architectural changes to the redesigned standard library and collections, along with covering in-depth type systems and first-level support for functions. You will discover how to leverage implicits as a primary mechanism for building type classes and look at different ways to test Scala code. You will also learn about abstract building blocks used in functional programming, giving you sufficient understanding to pick and use any existing functional programming library out there. In the concluding chapters, you will explore reactive programming by covering the Akka framework and reactive streams. By the end of this book, you will have built microservices and learned to implement them with the Scala and Lagom framework.
Table of Contents (19 chapters)

State monad

In imperative programming, we have the concept of global variables—variables that are available anywhere in the program. This approach is considered to be a bad practice, but is still used quite often. The concept of global state extends global variables by including system resources. As there is only one filesystem or system clock, it totally makes sense to make them globally and universally accessible from anywhere in the program code, right?

In JVM, some of these global resources are available via the java.lang.System class. It contains, for instance, references to "standard" input, output, and error streams, the system timer, environment variables, and properties. The global state should definitely be a good idea, then, if Java exposes it on a language level!

The problem with global state is that it breaks the referential transparency of the code...