Typical Kotlin (Kotlin Budapest User Group meetup - September)

The talk covers some of the basic built-in types of Kotlin (Any, Unit, Nothing), and how we interact with these types - whether we know it or not - when using basic constructs (the Elvis operator, return statements, null itself) of the language.

Transcript

1. Typical Kotlin Braun Márton Szabolcs zsmb.co zsmb13 braun.marton@autsoft.hu
2. Hello
3. Hello class
4. Hello class
5. Hello class class List<T>
6. Any The root of the hierarchy public open class Any { public open operator fun equals(other: Any?): Boolean public open fun hashCode(): Int public open fun toString(): String }
7. Any The root of the hierarchy
10. val maybeString: String? = null val definitelyString = maybeString ?: "replacement"
20. Unit public object Unit { override fun toString() = "kotlin.Unit" } The type with only one value
21. val noResult: Task< > Unit Unit The type with only one value fun () { // Empty! } empty() { // Empty! } Task< > noResult; Unit void Void : empty
22. Unit Unit The type with only one value void Void
23. Nothing A value that never exists public class Nothing private constructor()
24. Nothing A value that never exists fun loopy(): Nothing { while (true) { println("Loop!") } } fun exceptional(): Nothing { throw IllegalStateException() }
25. Nothing A value that never exists
26. Nothing The bottom type
27. Nothing The bottom type fun processData(data: List<String>) { // Use data } fun main(args: Array<String>) { val data: Nothing = loopy() processData(data) }
28. Nothing Elvis’ best friend fun calculate(someParam: Int?) { val x = someParam ?: exceptional() val y = x * 2 println(y) }
29. Nothing Elvis’ best friend
33. exceptional() Nothing Elvis’ best friend fun calculate(someParam: Int?) { val x = someParam ?: val y = x * 2 println(y) }
34. Nothing Elvis’ best friend throw IllegalArgumentException("!") fun calculate(someParam: Int?) { val x = someParam ?: val y = x * 2 println(y) }
35. * 2 someParam ?: return fun calculate(someParam: Int?) { val y = println(y) } Nothing Elvis’ best friend x val x =
36. someParam ?: return * 2 fun calculate(someParam: Int?) { val y = println(y) } someParam Nothing Elvis’ best friend
37. Nothing? Nothing.
38. Nothing? Nothing.
39. Nothing? Nothing. var x = null x = "foo" Type mismatch. Required: Nothing? Found: String
40. Nothing Edge cases fun oddity() { throw return return throw return }
41. Resources • Illustration style credit  http://natpryce.com/articles/000818.html • More about Nothing  http://oneeyedmen.com/nothing-can-save-us.html  https://blog.kotlin-academy.com/kotlins-nothing-its- usefulness-in-generics-5076a6a457f7
42. Questions? zsmb.co zsmb13 braun.marton@autsoft.hu