Table Of ContentLearn Scala Programming
A comprehensive guide covering functional and reactive
programming with Scala 2.13, Akka, and Lagom
Slava Schmidt
BIRMINGHAM - MUMBAI
Learn Scala Programming
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To my family – Tanja, Christina, and Marina – who made this book possible.
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Contributors
About the author
Slava Schmidt is a software developer living in Germany. During his career, he has used a
wide spectrum of programming languages, ranging from Assembler to Haskell, and
progressed from an intern programmer, via head of engineering, to a Scala contractor. In
his current role, he helps to develop and bring into production a number of Scala projects of
various sizes and complexities for customers from different industries.
He is a contributor to open source projects related to Scala and Akka. As a passionate
conference speaker, he regularly gives talks about technologies to share his experiences
with other developers.
I'd like to thank Tatjana Schmidt for making the images in this book look great, Mike
Litvin for his timely support, Marco Borst for (in)validating lots of ideas (without
necessarily knowing this) and the production team at Packt, especially Manjusha Mantri,
for all of their advice and assistance.
About the reviewers
Rambabu Posa has 14 years of rich experience in Scala, Java, and BigData ecosystems. He
has been working as Java developer since 2004 and Scala/BigData Developer since Mid of
2015. He loves functional programming in TDD (test-driven development) as a way of
developing reactive microservices. He loves teaching, and has provided online training and
written tutorials on Java, Scala, Cloud and BigData ecosystems. He loves developing
Reactive systems using Lightbend's Reactive Platform technology stack, including Lagom
Framework, ConductR, Scala, Akka Toolkit, Akka Streams, and Play Framework with
AWS. He is a master of Apache Kafka (Kafka, KStreams, Connect, Schema Registry, Mirror
Maker).
Mikhail Litvin is a passionate software engineer with more than 10 years experience in
systems analysis, software design, and software architecture. During the day, Mikhail
spends his time building highly scalable and resilient solutions for one of the leading
Europe, e-commerce companies. Mikhail works with a variety of technologies such as,
Scala, Akka, SQL/ NoSQL, AWS, Python, and others. He's interested in artificial intelligence
and machine learning.
In a spare time, Mikhail enjoys riding his bicycle, fishing, and traveling.
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Table of Contents
Preface 1
Chapter 1: An Introduction to Scala 2.13 8
Technical requirements 8
Introduction to Scala 2.13 8
New features of Scala 2.13 9
Optional parsing for string literals 9
Products can report the names of their element 10
Added methods for chaining operations 11
Automatic Resource Management 13
The Scala 2.13 Collection Library 14
IterableOnceOps 16
IterableOps 17
WithFilter 18
IterableFactory 19
View 19
Set 21
Map 23
SortedMap 24
HashMap 24
MultiMap 25
SeqMap 25
Seq 25
IndexedSeq 27
LinearSeq 28
Buffers 29
Scala Collection Contrib library 30
Summary 31
Questions 32
Further reading 32
Chapter 2: Understanding Types in Scala 33
Technical requirements 33
Understanding types 34
Ways to create a type 34
Literal types 35
Compound (intersection) types 38
Type constraints 39
Scala's types hierarchy and special types 40
Type inference 42
Path-dependent types 43
Table of Contents
Types – all the way down 45
Type parameters 45
Type members 46
Generalized type constraints 49
Infix types 49
Variance 50
Existential types 53
Higher kinded types 54
Type lambdas 55
Using types to define domain constraints 56
Phantom types 56
Self-recursive types 59
Summary 61
Questions 61
Further reading 62
Chapter 3: Deep Dive into Functions 63
Technical requirements 63
Ways to define a function 64
Function as a method 64
Local functions 66
Closures 67
Partial application and functions 68
Function literals 70
Currying 72
Polymorphism and higher order functions 72
Polymorphic functions 73
Higher-order functions 74
Recursion and trampolining 75
Recursion 76
Tail recursion 77
Trampolining 79
Object-oriented aspects of functions 80
Functions are traits 81
Partial functions 82
Function object 83
Extending functions 84
Summary 85
Questions 85
Further reading 86
Chapter 4: Getting to Know Implicits and Type Classes 87
Technical requirements 87
Types of implicits 88
Implicit conversions 88
[ ii ]
Table of Contents
Implicit parameters 91
Implicit classes 94
View and context bounds 95
View bounds 95
Context bounds 96
Type classes 97
Type classes 98
Type class recursive resolution 100
Type class variance 103
Implicit scope resolution 105
Lexical scope 106
Implicit scope 107
Static overloading rules 108
Summary 109
Questions 110
Further reading 110
Chapter 5: Property-Based Testing in Scala 111
Technical requirements 111
Introduction to property-based testing 112
From unit tests to properties 112
ScalaCheck 113
Properties 114
Types of properties 114
Commutativity 114
Associativity 115
Identity 116
Invariants 116
Idempotence 117
Induction 117
Symmetry 118
Test Oracle 118
Defining a property 119
Checking property 119
Combining properties 120
Generators 121
Existing generators 122
Combining generators 123
Shrinkers 126
Summary 128
Questions 129
Chapter 6: Exploring Built-In Effects 130
Technical requirements 130
Introduction to effects 131
Option 133
[ iii ]
