Practical Kotlin Deep Dive unpacks the “how” and “why” behind Kotlin from core language fundamentals and internal mechanisms to the design of its APIs. It spans Kotlin basics, the standard library, coroutines, kotlinx libraries, compiler internals, and Kotlin Multiplatform.

This book goes beyond surface-level APIs by diving into Kotlin’s internals: it walks through real Kotlin function implementations, demystifies generated bytecode, and explains how the Kotlin compiler interprets the language. It also draws directly from KEEP proposals, JetBrains YouTrack discussions, and compiler source code to connect concepts to their origins and design rationale. The result is an approach that helps you reason about Kotlin instead of simply memorizing APIs.

This progression ensures that you understand not only how to use Kotlin effectively, but also why the language was designed the way it is, giving you insights that translate directly into better code.

For continuous growth, the book includes curated references and additional resources so you can keep exploring beyond its pages. Complex or less common terms are explained with accessible footnotes, making advanced material approachable for newcomers while offering fresh insights to seasoned developers.

The "Pro Tips for Mastery" sections go beneath the surface, covering internal structures of Kotlin functions, algorithms, how the Kotlin compiler behaves, and implementation details that matter in real-world projects. Senior engineers will find thought-provoking details to sharpen their expertise, while mid-level developers gain insights for leveling up their Kotlin knowledge and building a stronger analytical mindset.

Whether you're optimizing performance-critical code, handling complex coroutine tasks, or exploring multiplatform development, this book challenges you to go beyond tutorials. Learn to reason about language design, understand internal mechanisms, and approach Kotlin development with clarity, curiosity, and confidence.

— Jaewoong Eum (skydoves)