Effective Kotlin
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Effective Kotlin

Best practices

About the Book

Kotlin is a powerful and pragmatic language, but it's not enough to know about its features. We also need to know when they should be used and in what way. This book is a guide for Kotlin developers on how to become excellent Kotlin developers. It presents and explains in-depth the best practices for Kotlin development. Each item is presented as a clear rule of thumb, supported by detailed explanations and practical examples.

If you are interested in paperback, you can purchase it here.

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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.

Marcin Moskała

Episode 254

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Reader Testimonials

Rafał Kuźmiński
Rafał Kuźmiński

Well done! I've read a few items and I have to admit that I learned some interesting stuff. Great book :)

Hanno Günther
Hanno Günther

Really love this book! ?

Hubert Kosacki
Hubert Kosacki

Some time ago I started reading @EffectiveKotlin by @marcinmoskala, it's a must-read for every developer writing Kotlin. Even if you don't agree with all the items, for sure it will make you think twice about what you're coding.

Archie David
Archie David

Thanks for writing Effective Kotlin, I'm liking the tips from the book so far.

Andy Gibel
Andy Gibel

I really enjoyed your Effective Kotlin book and intend to use it for an "Advanced Kotlin" workshop series I'm planning at work

Table of Contents

  • Introduction: Be pragmatic
  • Part 1: Good code
  • Chapter 1: Safety
    • Item 1: Limit mutability
    • Item 2: Minimize the scope of variables
    • Item 3: Eliminate platform types as soon as possible
    • Item 4: Do not expose inferred types
    • Item 5: Specify your expectations for arguments and states
    • Item 6: Prefer standard errors to custom ones
    • Item 7: Prefer a nullable or Result result type when the lack of a result is possible
    • Item 8: Handle nulls properly
    • Item 9: Close resources with use
    • Item 10: Write unit tests
  • Chapter 2: Readability
    • Item 11: Design for readability
    • Item 12: An operator’s meaning should be consistent with its function name
    • Item 13: Use operators to increase readability
    • Item 14: Specify the variable type when it is not clear
    • Item 15: Consider referencing receivers explicitly
    • Item 16: Properties should represent a state, not a behavior
    • Item 17: Consider naming arguments
    • Item 18: Respect coding conventions
  • Part 2: Code design
  • Chapter 3: Reusability
    • Item 19: Do not repeat knowledge
    • Item 20: Do not repeat common algorithms
    • Item 21: Use property delegation to extract common property patterns
    • Item 22: Use generics when implementing common algorithms
    • Item 23: Avoid shadowing type parameters
    • Item 24: Consider variance for generic types
    • Item 25: Reuse between different platforms by extracting common modules
  • Chapter 4: Abstraction design
    • Item 26: Each function should be written in terms of a single level of abstraction
    • Item 27: Use abstraction to protect code against changes
    • Item 28: Specify API stability
    • Item 29: Consider wrapping external APIs
    • Item 30: Minimize elements’ visibility
    • Item 31: Define contracts with documentation
    • Item 32: Respect abstraction contracts
  • Chapter 5: Object creation
    • Item 33: Consider factory functions instead of secondary constructors
    • Item 34: Consider a primary constructor with named optional arguments
    • Item 35: Consider defining a DSL for complex object creation
  • Chapter 6: Class design
    • Item 36: Prefer composition over inheritance
    • Item 37: Use the data modifier to represent a bundle of data
    • Item 38: Use function types or functional interfaces to pass operations and actions
    • Item 39: Use sealed classes and interfaces to express restricted hierarchies
    • Item 40: Prefer class hierarchies instead of tagged classes
    • Item 41: Use enum to represent a list of values
    • Item 42: Respect the contract of equals
    • Item 43: Respect the contract of hashCode
    • Item 44: Respect the contract of compareTo
    • Item 45: Consider extracting non-essential parts of your API into extensions
    • Item 46: Avoid member extensions
  • Part 3: Efficiency
  • Chapter 7: Make it cheap
    • Item 47: Avoid unnecessary object creation
    • Item 48: Use the inline modifier for functions with parameters of functional types
    • Item 49: Consider using inline value classes
    • Item 50: Eliminate obsolete object references
  • Chapter 8: Efficient collection processing
    • Item 51: Prefer Sequences for big collections with more than one processing step
    • Item 52: Consider associating elements to a map
    • Item 53: Consider using groupingBy instead of groupBy
    • Item 54: Limit the number of operations
    • Item 55: Consider Arrays with primitives for performance-critical processing
    • Item 56: Consider using mutable collections
  • Dictionary
  • Notes

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