Idiomatic Kotlin: Writing Efficient Code

Introduction

The book "Writing Idiomatic Kotlin" (authors Stephen Samuel and Stefan Bocutiu, 2017, 342 pages) is not another syntax reference, but a deep dive into the culture and style of the Kotlin language. In a world where Kotlin is rapidly replacing Java in Android development and backend projects, the ability to write not just working, but idiomatic code is becoming a key skill. This book teaches exactly that: how to use the language's capabilities 100% to make code concise, safe, and easy to read.

What This Book Is About

The authors do not waste time explaining basic syntax — it is assumed the reader is already familiar with the fundamentals of Kotlin. Instead, they focus on best practices and idioms that turn ordinary code into elegant solutions. The book covers a wide range of topics:

• Working with collections: using functions like map, filter, flatMap and others for a declarative style.
• Functional programming: lambdas, higher-order functions, immutability.
• Null safety: how to avoid NullPointerException using safe calls and the Elvis operator.
• Extension functions and properties: how to enrich existing classes without inheritance.
• Delegation: lazy initialization, delegated properties, delegates for patterns.
• Sealed classes and when expressions: modeling restricted hierarchies.
• Coroutines: asynchronous programming in an idiomatic style.
• Design patterns: how to implement Singleton, Builder, Strategy, and others in Kotlin style.
• Interoperability with Java: how to call Java from Kotlin and vice versa while maintaining idiomaticity.

Who This Book Is For

The book is aimed at developers already familiar with Kotlin (or Java) who want to take their language proficiency to the next level. It will be useful for:

• Android developers who want to write cleaner and more maintainable code.
• JVM backend developers (Spring, Ktor, etc.) striving to use all the features of Kotlin.
• Those transitioning from Java to Kotlin who want to avoid "Java thinking" in the new language.
• Programmers who already write in Kotlin but feel their code could be more concise and expressive.

What the Reader Will Learn

After reading the book, you will be able to:

• Write code that looks like it was written by an experienced Kotlin developer.
• Use functional constructs for data processing without loops and temporary variables.
• Effectively work with nullable types, avoiding runtime errors.
• Create DSL-like APIs using extension functions and lambdas with receivers.
• Apply delegation for lazy initialization, observable properties, and caching.
• Build asynchronous chains using coroutines without callback hell.
• Implement classic design patterns in a more compact and safe form.

Strengths

The main advantage of the book is its practical focus. Each chapter contains numerous code examples that can be immediately applied in a project. The authors do not just list the language's features, but show how to combine them to solve real-world problems. Particularly valuable is that the book teaches you to think in Kotlin, not just translate Java code into new syntax. The section on coroutines, although written before the release of stable version 1.3, provides a solid foundation for understanding asynchronous programming. Also worth noting is the quality explanation of sealed classes and when — these constructs are often underestimated by beginners.

Who Is Recommended

The book "Writing Idiomatic Kotlin" is an excellent choice for those who have already mastered the basics of Kotlin and want to move to the next level. It will be useful for both individual developers