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)

Type classes

The previous example demonstrated that we need three parts for context bounds to work:

  1. A parameterized type, T, which is defined as an implicit parameter of the function we're going to call
  2. One or more operations (methods) which are defined on T, and which will be available after the conversion
  3. Implicit instances that implement T

In the case of the type referred to of the method definition being an abstract one and the mentioned method being implemented in different ways in instances, we're talking about ad-hoc polymorphism (as opposed to parametric polymorphism for functions, and subtype polymorphism for subclasses). Here, we will explore how this concept is implemented with type classes, how the compiler finds suitable instances if needed, and how variance applies in ad hoc polymorphic cases.