Functional Programming in Go: Apply functional techniques in Golang to improve the testability, readability, and security of your code

 Cover....1

Preface....14

Title Page....2

Copyright....3

Dedication....4

Contributors....5

Table of Contents....8

Part 1: Functional Programming Paradigm Essentials....20

Chapter 1: Introducing Functional Programming....22

What is functional programming?....22

Introducing first-class functions....23

What are pure functions?....24

Say what you want, not how you want it    ....26

A brief history of functional programming....28

Modern functional programming....30

The Go programming paradigm....31

Why functional programming?....32

Why not functional programming in Go?....33

Comparing FP and OOP....34

Summary....35

Chapter 2: Treating Functions as First-Class Citizens....36

Benefits of first-class functions....36

Defining types for functions....37

Type aliases for primitives....37

Type aliases for functions....40

Using functions as objects....42

Passing functions to functions....42

In-line function definitions....43

Anonymous functions....43

Returning functions from functions....44

Functions in var....45

Functions inside data structures....46

Functions inside structs....47

Example 1 – map dispatcher....49

Creating a simple calculator....49

Example 2 – mocking functions for testing....51

Summary....55

Chapter 3: Higher-Order Functions....56

Technical requirements....57

An introduction to higher-order functions....57

Closures and variable scoping....57

Variable scoping in Go....58

Capturing variable context in functions (closures)....61

Partial application....63

Function currying, or how to reduce n-ary functions to unary functions....67

Example: function currying....69

Example: server constructor....70

Summary....74

Chapter 4: Writing Testable Code with Pure Functions....76

Technical requirements....76

What is purity?....77

Demonstrating pure versus impure function calls....77

Referential transparency....78

Idempotence....80

Statelessness....80

Side effects....80

Why does purity improve our code?....80

Increases the testability of our code....81

Increases the confidence in our code....83

Improved confidence in function names and signatures....84

Safer concurrency....85

When not to write pure functions....86

Input/output operations....86

Non-determinism can be desired....87

When we really have to panic!....87

How do we create pure functions?....87

Avoid global state....87

Separate pure and impure functionality....88

Example 1 – hotdog shop....90

Bad hotdog shop....90

Better hotdog shop....92

Summary....97

Chapter 5: Immutability....98

Technical requirements....98

What is immutability?....99

Immutability at the data layer....99

How to write immutable code in Go....100

Writing immutable code for collection data types....103

Measuring performance in mutable and immutable code....104

Benchmarking functions....104

Understanding stacks, heaps, and garbage collection....106

When to write mutable functions....109

What are functors and monads?....110

What’s a functor?....110

From functor to monad....112

Summary....115

Part 2: Using Functional Programming Techniques....116

Chapter 6: Three Common Categories of Functions....118

Technical requirements....118

Predicate-based functions....119

Implementing a Filter function....119

Any or all....123

Implementing DropWhile and TakeWhile....124

Map/transformation functions....126

Transformations while maintaining the data type....127

Data reducing functions....130

Example – working with airport data....134

Summary....137

Chapter 7: Recursion....138

Technical requirements....138

What is recursion?....139

Why do functional languages favor recursion?....141

When to use recursive functions....141

Iterating over trees....143

Recursion and functions as first-class citizens....146

Limits of recursive functions....151

Measuring the performance of recursive versus iterative solutions....151

Space limitation of recursive functions....153

Tail recursion as a solution to stack limitations....155

Summary....157

Chapter 8: Readable Function Composition with Fluent Programming....158

Technical requirements....158

Chaining functions through dot notation....159

Chaining methods for object creation (builder pattern)....159

Dot notation to chain functions on slices....161

Infinite data structures and lazy evaluation....170

Continuation-passing style programming....171

CPS and goroutines....177

When to use CPS?....178

Summary....178

Part 3: Design Patterns and Functional Programming Libraries....180

Chapter 9: Functional Design Patterns....182

Technical requirements....182

Classical design patterns in a functional paradigm....182

The strategy pattern....183

The decorator pattern....191

The Hollywood principle....195

Functional design patterns....197

Summary....199

Chapter 10: Concurrency and Functional Programming....200

Technical requirements....200

Functional programming and concurrency....201

Concurrency, parallelism, and distributed computing....201

Functional programming and concurrency....203

Creating concurrent functions....207

Concurrent filter implementation....207

Concurrent Map and FMap implementation....210

The pipeline pattern....214

Summary....222

Chapter 11: Functional Programming Libraries....224

Technical requirements....224

Is the library alive – and do the examples still match it?....225

Legal requirements....225

Pre-generics libraries for creating common FP functions....226

Code generation libraries for pre-generics Go....226

Post-generics functional programming libraries....232

Pie with generics....232

Lodash, for Go....234

Mo, for go....236

Summary....237

Index....238

About Packt....244

Other Books You May Enjoy....245

While Go is a multi-paradigm language that gives you the option to choose whichever paradigm works best for the particular problem you aim to solve, it supports features that enable you to apply functional principles in your code. In this book, you'll learn about concepts central to the functional programming paradigm and how and when to apply functional programming techniques in Go.

Starting with the basic concepts of functional programming, this Golang book will help you develop a deeper understanding of first-class functions. In the subsequent chapters, you'll gain a more comprehensive view of the techniques and methods used in functional languages, such as function currying, partial application, and higher-order functions. You'll then be able to apply functional design patterns for solving common programming challenges and explore how to apply concurrency mechanisms to functional programming.

By the end of this book, you'll be ready to improve your code bases by applying functional programming techniques in Go to write cleaner, safer, and bug-free code.

What You Will Learn:

• Gain a deeper understanding of functional programming through practical examples
• Build a solid foundation in core FP concepts and see how they apply to Go code
• Discover how FP can improve the testability of your code base
• Apply functional design patterns for problem solving
• Understand when to choose and not choose FP concepts
• Discover the benefits of functional programming when dealing with concurrent code

Who this book is for:

If you are a Go engineer with a background in traditionally object-oriented languages such as Java or C++ and want to broaden your knowledge of functional programming, this book is for you.