Programming Scala: Scalability = Functional Programming + Objects

Copyright
Table of Contents
Foreword
Foreword, Third Edition
Foreword, First and Second Edition
Preface
Welcome to Programming Scala, Third Edition
How to Read This Book
Welcome to Programming Scala, Second Edition
Welcome to Programming Scala, First Edition
Conventions Used in This Book
Using Code Examples
Getting the Code Examples
O’Reilly Online Learning
How to Contact Us
Acknowledgments for the Third Edition
Acknowledgments for the Second Edition
Acknowledgments for the First Edition
Chapter 1. Zero to Sixty: Introducing Scala
Why Scala?
The Appeal of Scala
Why Scala 3?
Migrating to Scala 3
Installing the Scala Tools You Need
Building the Code Examples
More Tips
Using sbt
Running the Scala Command-Line Tools Using sbt
A Taste of Scala
A Sample Application
Recap and What’s Next
Chapter 2. Type Less, Do More
New Scala 3 Syntax—Optional Braces
Semicolons
Variable Declarations
Ranges
Partial Functions
Method Declarations
Method Default and Named Parameters
Methods with Multiple Parameter Lists
Nesting Method Definitions and Recursion
Inferring Type Information
Repeated Parameter Lists
Language Keywords
Literal Values
Numeric Literals
Boolean Literals
Character Literals
String Literals
Symbol Literals
Function Literals
Tuples
Option, Some, and None: Avoiding Nulls
When You Really Can’t Avoid Nulls
Sealed Class Hierarchies and Enumerations
Organizing Code in Files and Namespaces
Importing Types and Their Members
Package Imports and Package Objects
Parameterized Types Versus Abstract Type Members
Recap and What’s Next
Chapter 3. Rounding Out the Basics
Defining Operators
Allowed Characters in Identifiers
Methods with Empty Parameter Lists
Operator Precedence Rules
Enumerations and Algebraic Data Types
Interpolated Strings
Scala Conditional Expressions
Conditional and Comparison Operators
for Comprehensions
for Loops
Generators
Guards: Filtering Values
Yielding New Values
Expanded Scope and Value Definitions
Scala while Loops
Using try, catch, and finally Clauses
Call by Name, Call by Value
Lazy Values
Traits: Interfaces and Mixins in Scala
When new Is Optional
Recap and What’s Next
Chapter 4. Pattern Matching
Safer Pattern Matching with Matchable
Values, Variables, and Types in Matches
Matching on Sequences
Pattern Matching on Repeated Parameters
Matching on Tuples
Parameter Untupling
Guards in Case Clauses
Matching on Case Classes and Enums
Matching on Regular Expressions
Matching on Interpolated Strings
Sealed Hierarchies and Exhaustive Matches
Chaining Match Expressions
Pattern Matching Outside Match Expressions
Problems in Pattern Bindings
Pattern Matching as Filtering in for Comprehensions
Pattern Matching and Erasure
Extractors
unapply Method
Alternatives to Option Return Values
unapplySeq Method
Implementing unapplySeq
Recap and What’s Next
Chapter 5. Abstracting Over Context: Type Classes and Extension Methods
Four Changes
Extension Methods
Build Your Own String Interpolator
Type Classes
Scala 3 Type Classes
Alias Givens
Scala 2 Type Classes
Scala 3 Implicit Conversions
Type Class Derivation
Givens and Imports
Givens Scoping and Pattern Matching
Resolution Rules for Givens and Extension Methods
The Expression Problem
Recap and What’s Next
Chapter 6. Abstracting Over Context: Using Clauses
Using Clauses
Context Bounds
Other Context Parameters
Context Functions
Constraining Allowed Instances
Implicit Evidence
Working Around Type Erasure with Using Clauses
Rules for Using Clauses
Improving Error Messages
Recap and What’s Next
Chapter 7. Functional Programming in Scala
What Is Functional Programming?
Functions in Mathematics
Variables That Aren’t
Functional Programming in Scala
Anonymous Functions, Lambdas, and Closures
Purity Inside Versus Outside
Recursion
Tail Calls and Tail-Call Optimization
Partially Applied Functions Versus Partial Functions
Currying and Uncurrying Functions
Tupled and Untupled Functions
Partial Functions Versus Functions Returning Options
Functional Data Structures
Sequences
Maps
Sets
Traversing, Mapping, Filtering, Folding, and Reducing
Traversing
Mapping
Flat Mapping
Filtering
Folding and Reducing
Left Versus Right Folding
Combinators: Software’s Best Component Abstractions
What About Making Copies?
Recap and What’s Next
Chapter 8. for Comprehensions in Depth
Recap: The Elements of for Comprehensions
for Comprehensions: Under the Hood
Translation Rules of for Comprehensions
Options and Container Types
Option as a Container?
Either: An Alternative to Option
Try: When There Is No Do
Validated from the Cats Library
Recap and What’s Next
Chapter 9. Object-Oriented Programming in Scala
Class and Object Basics: Review
Open Versus Closed Types
Classes Open for Extension
Overriding Methods? The Template Method Pattern
Reference Versus Value Types
Opaque Types and Value Classes
Opaque Type Aliases
Value Classes
Supertypes
Constructors in Scala
Calling Supertype Constructors
Export Clauses
Good Object-Oriented Design: A Digression
Fields in Types
The Uniform Access Principle
Unary Methods
Recap and What’s Next
Chapter 10. Traits
Traits as Mixins
Stackable Traits
Union and Intersection Types
Transparent Traits
Using Commas Instead of with
Trait Parameters
Should That Type Be a Class or Trait?
Recap and What’s Next
Chapter 11. Variance Behavior and Equality
Parameterized Types: Variance Under Inheritance
Functions Under the Hood
Variance of Mutable Types
Improper Variance of Java Arrays
Equality of Instances
The equals Method
The == and != Methods
The eq and ne Methods
Array Equality and the sameElements Method
Equality and Inheritance
Multiversal Equality
Case Objects and hashCode
Recap and What’s Next
Chapter 12. Instance Initialization and Method Resolution
Linearization of a Type Hierarchy
Initializing Abstract Fields
Overriding Concrete Fields
Abstract Type Members and Concrete Type Aliases
Recap and What’s Next
Chapter 13. The Scala Type Hierarchy
Much Ado About Nothing (and Null)
The scala Package
Products, Case Classes, Tuples, and Functions
Tuples and the Tuple Trait
The Predef Object
Implicit Conversions
Type Definitions
Condition Checking Methods
Input and Output Methods
Miscellaneous Methods
Recap and What’s Next
Chapter 14. The Scala Collections Library
Different Groups of Collections
Abstractions with Multiple Implementations
The scala.collection.immutable Package
The scala.collection.mutable Package
The scala.collection Package
The scala.collection.concurrent Package
The scala.collection.convert Package
The scala.collection.generic Package
Construction of Instances
The Iterable Abstraction
Polymorphic Methods
Equality for Collections
Nonstrict Collections: Views
Recap and What’s Next
Chapter 15. Visibility Rules
Public Visibility: The Default
Visibility Keywords
Protected Visibility
Private Visibility
Scoped Private and Protected Visibility
Recap and What’s Next
Chapter 16. Scala’s Type System, Part I
Parameterized Types
Abstract Type Members and Concrete Type Aliases
Comparing Abstract Type Members Versus Parameterized Types
Type Bounds
Upper Type Bounds
Lower Type Bounds
Context Bounds
View Bounds
Intersection and Union Types
Intersection Types
Union Types
Phantom Types
Structural Types
Refined Types
Existential Types (Obsolete)
Recap and What’s Next
Chapter 17. Scala’s Type System, Part II
Match Types
Dependently Typed Methods
Dependent Method and Dependent Function Types
Dependent Typing
Path-Dependent Types
Using this
Using super
Stable Paths
Self-Type Declarations
Type Projections
More on Singleton Types
Self-Recursive Types: F-Bounded Polymorphism
Higher-Kinded Types
Type Lambdas
Polymorphic Functions
Type Wildcard Versus Placeholder
Recap and What’s Next
Chapter 18. Advanced Functional Programming
Algebraic Data Types
Sum Types Versus Product Types
Properties of Algebraic Data Types
Final Thoughts on Algebraic Data Types
Category Theory
What Is a Category?
Functor
The Monad Endofunctor
The Semigroup and Monoid Categories
Recap and What’s Next
Chapter 19. Tools for Concurrency
The scala.sys.process Package
Futures
Robust, Scalable Concurrency with Actors
Akka: Actors for Scala
Actors: Final Thoughts
Stream Processing
Recap and What’s Next
Chapter 20. Dynamic Invocation in Scala
Structural Types Revisited
A Motivating Example: ActiveRecord in Ruby on Rails
Dynamic Invocation with the Dynamic Trait
DSL Considerations
Recap and What’s Next
Chapter 21. Domain-Specific Languages in Scala
Internal DSLs
External DSLs with Parser Combinators
About Parser Combinators
A Payroll External DSL
Internal Versus External DSLs: Final Thoughts
Recap and What’s Next
Chapter 22. Scala Tools and Libraries
Scala 3 Versions
Command-Line Interface Tools
Coursier
Managing Java JDKs with Coursier
The scalac Command-Line Tool
The scala Command-Line Tool
The scaladoc Command-Line Tool
Other Scala Command-Line Tools
Build Tools
Integration with IDEs and Text Editors
Using Notebook Environments with Scala
Testing Tools
Scala for Big Data: Apache Spark
Typelevel Libraries
Li Haoyi Libraries
Java and Scala Interoperability
Using Java Identifiers in Scala Code
Scala Identifiers in Java Code
Java Generics and Scala Parameterized Types
Conversions Between Scala and Java Collections
Java Lambdas Versus Scala Functions
Annotations for JavaBean Properties and Other Purposes
Recap and What’s Next
Chapter 23. Application Design
Recap of What We Already Know
Annotations
Using @main Entry Points
Design Patterns
Creational Patterns
Structural Patterns
Behavioral Patterns
Better Design with Design by Contract
The Parthenon Architecture
Recap and What’s Next
Chapter 24. Metaprogramming: Macros and Reflection
Scala Compile Time Reflection
Java Runtime Reflection
Scala Reflect API
Type Class Derivation: Implementation Details
Scala 3 Metaprogramming
Inline
Macros
Staging
Wrapping Up and Looking Ahead
Appendix A. Significant Indentation Versus Braces Syntax
Bibliography
Index
About the Author
Colophon