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
   

   View Slide

2. Hello
   

   View Slide

3. Hello
   class
   

   View Slide

4. Hello
   class
   

   View Slide

5. Hello
   class
   class List
   

   View Slide

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
   }
   

   View Slide

7. Any
   The root of the hierarchy
   

   View Slide

8. View Slide

9. View Slide

10. val maybeString: String? = null
    val definitelyString = maybeString ?: "replacement"
    

    View Slide

11. View Slide

12. View Slide

13. View Slide

14. View Slide

15. View Slide

16. View Slide

17. View Slide

18. View Slide

19. View Slide

20. Unit
    public object Unit {
    override fun toString() = "kotlin.Unit"
    }
    The type with only one value
    

    View Slide

21. val noResult: Task< >
    Unit
    Unit
    The type with only one value
    fun () {
    // Empty!
    }
    empty() {
    // Empty!
    }
    Task< > noResult;
    Unit void
    Void
    :
    empty
    

    View Slide

22. Unit
    Unit
    The type with only one value
    void
    Void
    

    View Slide

23. Nothing
    A value that never exists
    public class Nothing private constructor()
    

    View Slide

24. Nothing
    A value that never exists
    fun loopy(): Nothing {
    while (true) {
    println("Loop!")
    }
    }
    fun exceptional(): Nothing {
    throw IllegalStateException()
    }
    

    View Slide

25. Nothing
    A value that never exists
    

    View Slide

26. Nothing
    The bottom type
    

    View Slide

27. Nothing
    The bottom type
    fun processData(data: List) {
    // Use data
    }
    fun main(args: Array) {
    val data: Nothing = loopy()
    processData(data)
    }
    

    View Slide

28. Nothing
    Elvis’ best friend
    fun calculate(someParam: Int?) {
    val x = someParam ?: exceptional()
    val y = x * 2
    println(y)
    }
    

    View Slide

29. Nothing
    Elvis’ best friend
    

    View Slide

30. View Slide

31. View Slide

32. View Slide

33. exceptional()
    Nothing
    Elvis’ best friend
    fun calculate(someParam: Int?) {
    val x = someParam ?:
    val y = x * 2
    println(y)
    }
    

    View Slide

34. Nothing
    Elvis’ best friend
    throw IllegalArgumentException("!")
    fun calculate(someParam: Int?) {
    val x = someParam ?:
    val y = x * 2
    println(y)
    }
    

    View Slide

35. * 2
    someParam ?: return
    fun calculate(someParam: Int?) {
    val y =
    println(y)
    }
    Nothing
    Elvis’ best friend
    x
    val x =
    

    View Slide

36. someParam ?: return
    * 2
    fun calculate(someParam: Int?) {
    val y =
    println(y)
    }
    someParam
    Nothing
    Elvis’ best friend
    

    View Slide

37. Nothing?
    Nothing.
    

    View Slide

38. Nothing?
    Nothing.
    

    View Slide

39. Nothing?
    Nothing.
    var x = null
    x = "foo"
    Type mismatch.
    Required: Nothing?
    Found: String
    

    View Slide

40. Nothing
    Edge cases
    fun oddity() {
    throw return return throw return
    }
    

    View Slide

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
    

    View Slide

42. Questions?
    zsmb.co zsmb13
    braun.marton@autsoft.hu
    

    View Slide