Functional Kotlin
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Functional Kotlin

About the Book

This book is about functional programming features in Kotlin. It first covers the essentials, and then it builds on them: it presents important and practical topics like collection processing, function references, scope functions, DSL usage and creation, and context receivers.

This position is perfect for developers who know the basics of Kotlin and want to learn well a bit more advanced features. It is a natural continuation of Kotlin for developers: Essentials.

It is based on the second day of the Kotlin for developers workshop and serves as one of the official workbooks for the workshop.

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.

Table of Contents

    • Introduction
      • Who is this book for?
      • What will be covered?
      • Kotlin for developers
      • Code conventions
      • Acknowledgments
    • Introduction to functional programming with Kotlin
      • Why do we need to use functions as objects?
    • Function types
      • Defining function types
      • Using function types
      • Named parameters
      • Type aliases
      • A function type is an interface
    • Anonymous functions
    • Lambda expressions
      • Tricky braces
      • Parameters
      • Trailing lambdas
      • Result values
      • Lambda expression examples
      • An implicit name for a single parameter
      • Closures
      • Lambda expressions vs anonymous functions
    • Function references
      • Top-level functions references
      • Method references
      • Extension function references
      • Method references and generic types
      • Bounded function references
      • Constructor references
      • Bounded object declaration references
      • Function overloading and references
      • Property references
    • SAM Interface support in Kotlin
      • Support for Java SAM interfaces in Kotlin
      • Functional interfaces
    • Inline functions
      • Inline functions
      • Inline functions with functional parameters
      • Non-local return
      • Crossinline and noinline
      • Reified type parameters
      • Inline properties
      • Costs of the inline modifier
      • Using inline functions
    • Collection processing
      • forEach and onEach
      • filter
      • map
      • flatMap
      • fold
      • reduce
      • sum
      • withIndex and indexed variants
      • take, takeLast, drop, dropLast and subList
      • Getting elements at certain positions
      • Finding an element
      • Counting: count
      • any, all and none
      • partition
      • groupBy
      • Associating: associate, associateBy and associateWith
      • distinct and distinctBy
      • Sorting: sorted, sortedBy and sortedWith
      • Sorting mutable collections
      • Maximum and minimum
      • shuffled and random
      • zip and zipWithNext
      • Windowing
      • joinToString
      • Map, Set and String processing
      • Using them all together
    • Sequences
      • What is a sequence?
      • Order is important
      • Sequences do the minimum number of operations
      • Sequences can be infinite
      • Sequences do not create collections at every processing step
      • When aren’t sequences faster?
      • What about Java streams?
      • Kotlin Sequence debugging
      • Summary
    • Type Safe DSL Builders
      • A function type with a receiver
      • Simple DSL builders
      • Using apply
      • Multi-level DSLs
      • DslMarker
      • A more complex example
      • When should we use DSLs?
      • Summary
    • Scope functions
      • let
      • also
      • takeIf and takeUnless
      • apply
      • The dangers of careless receiver overloading
      • with
      • run
      • Using scope functions
    • Context receivers
      • Extension function problems
      • Introducing context receivers
      • Use cases
      • Classes with context receivers
      • Concerns
      • Summary
    • A birds-eye view of Arrow
      • Functions and Arrow Core
      • Testing higher-order functions
      • Error Handling
      • Data Immutability with Arrow Optics
  • Notes

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