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Learn Scala Programming
Learn Scala Programming

Learn Scala Programming: A comprehensive guide covering functional and reactive programming with Scala 2.13, Akka, and Lagom

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Learn Scala Programming

Understanding Types in Scala

The strong type system is one of the most important parts of the Scala language. Like a double-edged sword, it helps the compiler to verify and optimize the code on one side, while at the same time guiding developers toward possible correct implementations and preventing them from making programming mistakes on another side. As with any sharp tool, it requires some skill so that it can be used for carving beautiful source code without cutting the user in the process.

In this chapter, we will improve this skill by recapping and summarizing basic type-related knowledge, taking a look at a new type that was introduced in Scala 2.13, and finally looking at some advanced usages of types.

The following topics will be covered in this chapter:

  • Different ways to create a type
  • Different ways to parameterize a type
  • Kinds of types
  • Using types to express domain...

Technical requirements

Understanding types

The type of something is a summation of the information the compiler owns about this something. In the most general case, we're talking about the type of a variable; the knowledge of the compiler includes the methods that are available on this variable and the classes that the variable extends. A very convenient feature of Scala is that it tries to use type inference where possible, freeing the developer from the need to define types explicitly.

Let's take a structured look at Scala's type system, starting with a short recap of its basics.

Ways to create a type

There are four ways to define a type in Scala:

  • By using a literal to define a singleton type
  • By using the type keyword to define...

Types – all the way down

Up until now, we have only talked about concrete types. Despite being quite simple, they already allow for the expression of a lot of properties of a program on the type level and they have these properties verified at compile time. Scala gives the developer even more freedom by allowing them to use types as parameters while defining methods, classes, or other types. In the next section, we will look at different ways to do this, starting with basic type parameters and type member definition, and continuing with type constraints and variance topics. We'll conclude our discussion with higher kinded types and type lambdas.

Type parameters

Type parameters are defined using square brackets...

Using types to define domain constraints

We've already seen how simple types can be used to express domain constraints, as discussed in the Path-dependent types section. We implemented a lock that guaranteed at compile time that it is only possible to open and close it with the key created for this specific lock. We will conclude our study of type parameters and higher kinded types with two examples.

The first example will demonstrate an application of phantom types to create another version of the lock, which can guarantee the safety of state transitions at compile time without the use of inheritance.

The second example will show how self-recursive types can help to constrain possible subtyping.

Phantom types

The phantom...

Summary

The type system is one of the key components of the Scala language. It allows the developer to express expectations about the behavior of the program, which can then be checked at compile time. This reduces the number of tests needed to verify the correctness of the solution and the possibility of runtime errors.

Usually, strictly typed languages are associated with verbose code. Normally, this is not the case with Scala because of its powerful type inference mechanism.

Scala allows you to define very narrow types containing a single value as well as much wider types, even those represented as a combination of other types.

The type definition can be made more precise by using type constraints, type parameters, and variance.

We also looked at some examples of how the type system can be used to express domain constraints.

Needless to say, Scala's ecosystem is much richer...

Questions

  1. Which type constraints can you name?
  2. What implicit type constraints are added to a type if there are no type constraints defined on it by the developer?
  3. Which operators can be used to refer to the nested type of some type?
  4. Which type can be used as an infix type?
  5. Why is the use of structural types discouraged in Scala?
  6. What is expressed via variance?

Further reading

  • Mads Hartmann, and Ruslan Shevchenko, Professional Scala: You will learn how to write type-safe code concisely and expressively in an environment that lets you build for the JVM, browser, and more.

  • Vikash Sharma, Learning Scala Programming: Learn how to write scalable and concurrent programs in Scala, a language that grows with you.
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Key benefits

  • Develop a strong foundation in functional programming and Scala's Standard Library (STL)
  • Get a detailed coverage of Lightbend Lagom—the latest microservices framework from Lightbend
  • Understand the Akka framework and learn event-based Programming with Scala

Description

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.

Who is this book for?

This book is for beginner to intermediate level Scala developers who would like to advance and gain knowledge of the intricacies of the Scala language, expand their functional programming tools, and explore actor-based concurrency models.

What you will learn

  • Acquaint yourself with the new standard library of Scala 2.13
  • Get to grips with the Grok functional paradigms
  • Get familiar with type system to express domain constraints
  • Understand the actor model and different Akka libraries
  • Grasp the concept of building microservices using Lagom framework
  • Deep dive into property-based testing and its practical applications
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Publication date : Oct 31, 2018
Length: 498 pages
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Language : English
ISBN-13 : 9781788836302
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Table of Contents

18 Chapters
An Introduction to Scala 2.13 Chevron down icon Chevron up icon
Understanding Types in Scala Chevron down icon Chevron up icon
Deep Dive into Functions Chevron down icon Chevron up icon
Getting to Know Implicits and Type Classes Chevron down icon Chevron up icon
Property-Based Testing in Scala Chevron down icon Chevron up icon
Exploring Built-In Effects Chevron down icon Chevron up icon
Understanding Algebraic Structures Chevron down icon Chevron up icon
Dealing with Effects Chevron down icon Chevron up icon
Familiarizing Yourself with Basic Monads Chevron down icon Chevron up icon
A Look at Monad Transformers and Free Monad Chevron down icon Chevron up icon
An Introduction to the Akka and Actor Models Chevron down icon Chevron up icon
Building Reactive Applications with Akka Typed Chevron down icon Chevron up icon
Basics of Akka Streams Chevron down icon Chevron up icon
Project 1 - Building Microservices with Scala Chevron down icon Chevron up icon
Project 2 - Building Microservices with Lagom Chevron down icon Chevron up icon
Preparing the Environment and Running Code Samples Chevron down icon Chevron up icon
Assessments Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Half star icon Empty star icon Empty star icon Empty star icon 1.5
(2 Ratings)
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2 star 50%
1 star 50%
F. Salvi Aug 03, 2021
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I don't like the book's style. It as reading a scaladoc...
Amazon Verified review Amazon
Martin Jasny Jan 02, 2019
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The name of this book is utterly misleading. It is only for advanced users of Scala! It only lists the new features of the version 2.13. The version 2.13 is not even out at the time of the writing. It assumes that the user knows Scala fairly well.The first chapter summarizes the new feature of 2.13, especially with respect to the collectionsThe second chapter deal with types in Scala without properly defining or introducing them, again with respect to the version 2.13.And so on. If the version 2.14 is out, the book is useless.The book uses SBT.I have added it to my Safari bookshelf because of the mainly functional view of the language, and dealing with collections and monads. But the treatment of the collections is incomplete and the chapters on monads are useless. Anyway, I have not wasted any money, I have only wasted my bookshelf slot for 30 days.So I have been frustrated and this review reflects my frustration. May be some readers find this book useful. But think twice and check the preview on the Amazon sales page thoroughly before you buy it.
Amazon Verified review Amazon
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