Advanced Kotlin
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Advanced Kotlin

About the Book

You can be a developer - even a good one - without understanding the topics explained in this book, but at some point, you’ll need it. You are likely using tools made using features described in this book every day, such as libraries based on annotation processing or compiler plugins, classes that use variance modifiers, functions with contracts, or property delegates, but do you understand these features? Would you be able to implement similar tools yourself? Would you be able to analyze and debug them? This book will make all this possible for you. It focuses exclusively on the most advanced Kotlin topics, which are often not well understood even by senior Kotlin developers. It should equip you with the knowledge you need and show you possibilities you never before imagined. I hope you enjoy it as much as I enjoyed writing it.

About the Author

Marcin Moskała
Marcin Moskała

Marcin Moskala is an experienced developer and Kotlin trainer. He is the founder of the Kt. Academy, Kotlin GDE, an official JetBrains partner for teaching Kotlin, and author of the books Effective Kotlin, Kotlin Coroutines, and Android Development with Kotlin.

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Table of Contents

  • Introduction
    • Who is this book for?
    • The structure of this book
    • That will be covered?
    • The Kotlin for Developers series
    • Conventions
    • Code conventions
    • Acknowledgments
  • Part 1: Advanced Kotlin features
  • Generic variance modifiers
    • List variance
    • Consumer variance
    • Function types
    • Exercise: Usage of generic types
    • The Covariant Nothing Object
    • The Covariant Nothing Class
    • Variance modifier limitations
    • UnsafeVariance annotation
    • Variance modifier positions
    • Star projection
    • Summary
    • Exercise: Generic Response
    • Exercise: Generic Consumer
  • Interface delegation
    • The delegation pattern
    • Delegation and inheritance
    • Kotlin interface delegation support
    • Wrapper classes
    • The decorator pattern
    • Intersection types
    • Limitations
    • Conflicting elements from parents
    • Summary
    • Exercise: ApplicationScope
  • Property delegation
    • How property delegation works
    • Other getValue and setValue parameters
    • Implementing a custom property delegate
    • Provide a delegate
    • Property delegates in Kotlin stdlib
    • The notNull delegate
    • Exercise: Lateinit delegate
    • The lazy delegate
    • Exercise: Blog Post Properties
    • The observable delegate
    • The vetoable delegate
    • A map as a delegate
    • Review of how variables work
    • Summary
    • Exercise: Mutable lazy delegate
  • Kotlin Contracts
    • The meaning of a contract
    • How many times do we invoke a function from an argument?
    • Implications of the fact that a function has returned a value
    • Using contracts in practice
    • Summary
    • Exercise: Coroutine time measurement
  • Part 2: Kotlin on different platforms
  • Java interoperability
    • Nullable types
    • Kotlin type mapping
    • JVM primitives
    • Collection types
    • Annotation targets
    • Static elements
    • JvmField
    • Using Java accessors in Kotlin
    • JvmName
    • JvmMultifileClass
    • JvmOverloads
    • Unit
    • Function types and function interfaces
    • Tricky names
    • Throws
    • JvmRecord
    • Summary
    • Exercise: Adjust Kotlin for Java usage
  • Using Kotlin Multiplatform
    • Multiplatform module configuration
    • Expect and actual elements
    • Possibilities
    • Multiplatform libraries
    • A multiplatform mobile application
    • Summary
    • Exercise: Multiplatform LocalDateTime
  • JavaScript interoperability
    • Setting up a project
    • Using libraries available for Kotlin/JS
    • Using Kotlin/JS
    • Building and linking a package
    • Distributing a package to npm
    • Exposing objects
    • Exposing Flow and StateFlow
    • Adding npm dependencies
    • Frameworks and libraries for Kotlin/JS
    • JavaScript and Kotlin/JS limitations
    • Summary
    • Exercise: Migrating a Kotlin/JVM project to KMP
  • Part 3: Metaprogramming
  • Reflection
    • Hierarchy of classes
    • Function references
    • Parameter references
    • Property references
    • Class reference
    • Serialization example
    • Referencing types
    • Type reflection example: Random value
    • Kotlin and Java reflection
    • Breaking encapsulation
    • Summary
    • Exercise: Function caller
    • Exercise: Object serialization to JSON
    • Exercise: Object serialization to XML
    • Exercise: DSL-based dependency injection library
  • Annotation processing
    • Your first annotation processor
    • Hiding generated classes
    • Summary
    • Exercise: Annotation Processing execution measurement wrapper
  • Kotlin Symbol Processing
    • Your first KSP processor
    • Testing KSP
    • Dependencies and incremental processing
    • Multiple rounds processing
    • Using KSP on multiplatform projects
    • Summary
    • Exercise: KSP execution measurement wrapper
  • Kotlin Compiler Plugins
    • Compiler frontend and backend
    • Compiler extensions
    • Popular compiler plugins
    • Making all classes open
    • Changing a type
    • Generate function wrappers
    • Example plugin implementations
    • Summary
  • Static Code Analysers
    • What are Static Analysers?
    • Types of analysers
    • Kotlin Code Analysers
    • Setting up detekt
    • Writing your first detekt Rule
    • Conclusion
  • Ending
  • Exercise solutions
  • Notes

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