Functional Programming in Swift: From Basics to Advanced Patterns

This book is a practical guide to functional programming (FP) in Swift for iOS and macOS developers. Unlike many resources that treat FP as abstract theory, this edition focuses on concrete techniques applicable in everyday development.

You will learn how a functional approach helps write more predictable, testable, and concurrently executable code. Swift, being a multi-paradigm language, provides excellent opportunities for applying FP — from closures and generics to protocols with Associated Types.

What you will find in the book:

• FP Basics: pure functions, immutability, absence of side effects.
• Working with Collections: map, flatMap, filter, reduce — not just syntax, but a philosophy of data processing.
• Optional Types as Monads: deep understanding of Optional, chaining, and working with nil.
• Function Composition: building complex operations from simple functions.
• Advanced Patterns: functors, applicative functors, monads (Result, Future, Promise).
• Reactive Programming: the connection of FP with Combine and RxSwift.
• Testing: how functional code simplifies writing unit tests.

Who this book is for:

• iOS/macOS developers with 1+ year of experience who want to go beyond MVC and UIKit.
• Developers familiar with OOP but wanting to master an alternative paradigm.
• Those who want to write code that is easy to refactor and maintain.

The book contains numerous code examples that can be immediately applied in real projects. You will learn to avoid mutable state, effectively use closures, and build application architecture based on functional principles. Special attention is given to practical scenarios: handling network requests, working with Core Data, animation, and UI logic.

After reading, you will be able to confidently combine OOP and FP, choosing the best tool for each task, and write Swift code that works reliably in multithreaded environments.