Introduction to Functional Programing in Kotlin and Arrow

Transcript

1. Welcome
2. Introduction to Functional Programing in Kotlin and Arrow Hadi Tok Google Developers Expert (Android) Technical Lead, @CitizenMe https://haditok.com/
3. Functional Programming
4. Functional Programming In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data.* *https://mauriziostorani.wordpress.com/2008/08/29/functional-programming-examples-methods-and-concepts/
5. Functional Programming In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data.
6. Functional Programming In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data.
7. Mathematical Functions A function is a relation for which each value from the set the first components of the ordered pairs is associated with exactly one value from the set of second components of the ordered pair.
8. Function { 1, 2, 3, 4} {A, B, C}
9. Function { 1, 2, 3, 4} {A, B, C}
10. Function { 1, 2, 3, 4} {A, B, C}
11. Functional Programming In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data.
12. State class MyClass{ var list = listOf(1,2,3,4,5) fun filterList() { list = list.filter { it%2 !=0 } } }
13. State class MyClass{ val list = listOf(1,2,3,4,5) fun filterList(list:List<Int>): List<Int> { return list.filter { it!=0 } } }
14. Functional Programming In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data.
15. Mutable data fun filterList(list:List<Int>){ val iterator=list.iterator() for(i in iterator){ if(i%2==0){ iterator.remove() } } }
16. Mutable data val filteredList = list.filter { it % 2 != 0 }
17. Changes in state and data • Who is the owner of the data? • What would happen when data changes? • Should other constructs using the data needs to be notified? • How other constructs will be notified? • What happens when there are multiple changes at the same time?
18. Pure functions • Its return value is the same for the same arguments • Has no side effects
19. Side effects • Mutation of local static variables,non-local variables, mutable reference arguments • Throwing an exception • I/O operations
20. Kotlin and Functional Programming
21. Package Level Functions class Logger{ fun log(message: String){ println(message) } }
22. Package Level Functions fun log(message: String){ println(message) }
23. interface Callback{ fun onComplete() } fun operationWithACallBack(callback: Callback){ Thread.sleep(1000L) callback.onComplete() } Higher order Functions
24. operationWithACallBack(object : Callback{ override fun onComplete() { println("completed") } }) Higher order Functions
25. fun operationWithACallBack(callback: () -> Unit) { Thread.sleep(1000L) callback() } Higher order Functions
26. operationWithACallBack ({ println("completed") }) Higher order Functions
27. operationWithACallBack(){ println("completed") } Higher order Functions
28. operationWithACallBack{ println("completed") } Higher order Functions
29. data class Customer( val name: String, val city: String ) Higher order Functions
30. fun printCustomerByCity(city: String) { val filteredCustomers = customers.filter { it.city == city } filteredCustomers.forEach { println(it) } } fun printCustomerByName(name: String) { val filteredCustomers = customers.filter { it.name == name } filteredCustomers.forEach { println(it) } } Higher order Functions
31. fun printCustomers(predicate: (Customer) -> Boolean) { val filteredCustomer = customers.filter(predicate) filteredCustomers.forEach { println(it) } } fun main(args: Array<String>) { printCustomers { it.city == "Istanbul" } printCustomers { it.name == "Hadi" } } Higher order Functions
32. object StringUtils { fun getThirdCharacter(string: String): Char { if(string.length>2){ return string[2] } throw IllegalArgumentException() } } Extension Functions
33. val thirdLetter = StringUtils.getThirdCharacter("Kotlin") Extension Functions
34. fun String.getThirdCharacter(): Char { if(length>2){ return get(2) } throw IllegalArgumentException() } Extension Functions
35. val thirdCharacter = "Kotlin".getThirdCharacter() Extension Functions
36. list.forEach { println(it) } Extension Functions
37. public inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit { for (element in this) action(element) } Extension Functions
38. Arrow Λrrow is a library for Typed Functional Programming in Kotlin. https://arrow-kt.io
39. Arrow Arrow aims to provide a lingua franca of interfaces and abstractions across Kotlin libraries. For this, it includes the most popular data types, type classes and abstractions such as Option, Either, IO, Functor, Applicative, Monad to empower users to write pure FP apps and libraries built atop higher order abstractions. https://arrow-kt.io
40. fun tryGetThirdCharacter(string:String): Try<Char> { return Try { if(string.length<2){ throw IllegalArgumentException("string is short") }else{ string[3] } } } Try
41. tryGetThirdCharacer("Kotlin") .getOrElse { println(it.message) } Try
42. val thirdCharacter = tryGetThirdLetter("Go") .getOrDefault { "a" } Try
43. tryGetThirdLetter("Kotlin") .fold( { println(it.message) }, { println("third char is $it") } ) Try
44. fun getMessage(useResource: Boolean): Either<String, Int> { return if (useResource) { Either.right(R.string.start) } else { Either.left("Start") } } Either
45. val textEither = getMessage(useResource) val text: String = when (textEither) { is Either.Left -> textEither.a is Either.Right -> getString(textEither.b) } Either
46. fun divide(x: Int, y: Int): Option<Int> { return if (y == 0) { Option.empty() } else { Option.just(x / y) } } Option
47. val result = divide(x,y).map { it*6 } Option
48. Thank you