Functional Kotlin by Marcin Moskała

Description

This book is about functional programming features in Kotlin. It first covers the essentials and then builds on them: it presents important and practical topics like collection processing, scope functions, and DSL usage and creation, context receivers. 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. Introduction Who is this book for? What will be covered? The Kotlin for Developers series 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