Kotlin

1. The Feel of Kotlin
Dmitry Jemerov <yole@jetbrains.com>

2. What’s Kotlin?

3. What’s Kotlin?
• Statically typed programming language

4. What’s Kotlin?
• Statically typed programming language
• Targets JVM, Android and Web

5. What’s Kotlin?
• Statically typed programming language
• Targets JVM, Android and Web
• In development since mid-2010

6. Why Kotlin?
• Concise
• Expressive
• Safe
• Develop with Pleasure!

7. Why Not
<other JVM language>?

8. Why Not
<other JVM language>?
• 100% Java interoperability

9. Why Not
<other JVM language>?
• 100% Java interoperability
• 100% Java performance

10. Why Not
<other JVM language>?
• 100% Java interoperability
• 100% Java performance
• Smooth learning curve

11. Why Not
<other JVM language>?
• 100% Java interoperability
• 100% Java performance
• Smooth learning curve
• Maintaining existing investment

12. Why Not
<other JVM language>?
• 100% Java interoperability
• 100% Java performance
• Smooth learning curve
• Maintaining existing investment
• Focus on developer tools

13. Kotlin at JetBrains

14. Kotlin at JetBrains
• Kotlin itself

15. Kotlin at JetBrains
• Kotlin itself
• Customer portal

16. Kotlin at JetBrains
• Kotlin itself
• Customer portal
• Plugins for IntelliJ IDEA, TeamCity

17. Kotlin at JetBrains
• Kotlin itself
• Customer portal
• Plugins for IntelliJ IDEA, TeamCity
• YouTrack v.next

18. Kotlin at JetBrains
• Kotlin itself
• Customer portal
• Plugins for IntelliJ IDEA, TeamCity
• YouTrack v.next
• Major new product (unannounced)

19. Hello World
package helloWorld
fun main(args: Array<String>) {
println("Hello ${args[0]}")
}

20. Hello World
package helloWorld
fun main(args: Array<String>) {
println("Hello ${args[0]}")
}

21. Hello World
package helloWorld
fun main(args: Array<String>) {
println("Hello ${args[0]}")
}

22. Hello World
package helloWorld
fun main(args: Array<String>) {
println("Hello ${args[0]}")
}

23. Classes
class Person(val firstName: String,
val lastName: String) {
val fullName: String
get() = "$firstName $lastName"
}

24. Classes
class Person(val firstName: String,
val lastName: String) {
val fullName: String
get() = "$firstName $lastName"
}

25. Traits and Objects
trait Expr
class Constant(val value: Double) : Expr
class Sum(val op1: Expr, val op2: Expr)
: Expr
object NotANumber : Expr

26. Traits and Objects
trait Expr
class Constant(val value: Double) : Expr
class Sum(val op1: Expr, val op2: Expr)
: Expr
object NotANumber : Expr

27. Traits and Objects
trait Expr
class Constant(val value: Double) : Expr
class Sum(val op1: Expr, val op2: Expr)
: Expr
object NotANumber : Expr

28. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

29. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

30. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

31. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

32. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

33. Extension Functions
fun Expr.eval(): Double = when(this) {
is Constant -> value
is Sum -> op1.eval() + op2.eval()
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

34. Extension Functions
fun Expr.eval(): Double = when(this) {
is Constant -> value
is Sum -> op1.eval() + op2.eval()
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

35. Extension Functions
fun Expr.eval(): Double = when(this) {
is Constant -> value
is Sum -> op1.eval() + op2.eval()
NotANumber -> Double.NaN
else ->
throw IllegalArgumentException()
}

36. Operator Overloading
fun Expr.plus(rhs: Expr)
= Sum(this, rhs)
val Double.toExpr: Expr
get() = Constant(this)
fun exprTest() {
val expr = 1.0.toExpr + 2.0.toExpr
println(eval(expr))
}

37. Operator Overloading
fun Expr.plus(rhs: Expr)
= Sum(this, rhs)
val Double.toExpr: Expr
get() = Constant(this)
fun exprTest() {
val expr = 1.0.toExpr + 2.0.toExpr
println(eval(expr))
}

38. Operator Overloading
fun Expr.plus(rhs: Expr)
= Sum(this, rhs)
val Double.toExpr: Expr
get() = Constant(this)
fun exprTest() {
val expr = 1.0.toExpr + 2.0.toExpr
println(eval(expr))
}

39. Operator Overloading
fun Expr.plus(rhs: Expr)
= Sum(this, rhs)
val Double.toExpr: Expr
get() = Constant(this)
fun exprTest() {
val expr = 1.0.toExpr + 2.0.toExpr
println(eval(expr))
}

40. Operator Overloading
fun Expr.plus(rhs: Expr)
= Sum(this, rhs)
val Double.toExpr: Expr
get() = Constant(this)
fun exprTest() {
val expr = 1.0.toExpr + 2.0.toExpr
println(eval(expr))
}

41. Nullability
open class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
val parentDepth = if (parent != null)
parent.depth()
else
0
return parentDepth + 1
}
}

42. Nullability
open class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
val parentDepth = if (parent != null)
parent.depth()
else
0
return parentDepth + 1
}
}

43. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
return (parent?.depth() ?: 0) + 1
}
}

44. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
return (parent?.depth() ?: 0) + 1
}
}

45. Elvis Return
fun TreeNode.isBalanced(): Boolean {
val l = left?.depth() ?: return false
val r = right?.depth() ?: return false
return l == r
}

46. Default Parameter Values
fun List<String>.join(sep: String = ", ")
: String {
val sb = StringBuilder()
for (i in 0..size()-1) {
if (i > 0) sb.append(sep)
sb.append(this[i])
}
return sb.toString()
}

47. Default Parameter Values
fun List<String>.join(sep: String = ", ")
: String {
val sb = StringBuilder()
for (i in 0..size()-1) {
if (i > 0) sb.append(sep)
sb.append(this[i])
}
return sb.toString()
}

48. Default Parameter Values
fun List<String>.join(sep: String = ", ")
: String {
val sb = StringBuilder()
for (i in 0..size()-1) {
if (i > 0) sb.append(sep)
sb.append(this[i])
}
return sb.toString()
}

49. Maps
val developers = mapOf(
"Kotlin" to "Andrey",
"Python" to "Guido")
fun report() {
for((language, author) in developers) {
println("$author made $language")
}
println("${developers["Kotlin"]} rocks")
}

50. Maps
val developers = mapOf(
"Kotlin" to "Andrey",
"Python" to "Guido")
fun report() {
for((language, author) in developers) {
println("$author made $language")
}
println("${developers["Kotlin"]} rocks")
}

51. Maps
val developers = mapOf(
"Kotlin" to "Andrey",
"Python" to "Guido")
fun report() {
for((language, author) in developers) {
println("$author made $language")
}
println("${developers["Kotlin"]} rocks")
}

52. Maps
val developers = mapOf(
"Kotlin" to "Andrey",
"Python" to "Guido")
fun report() {
for((language, author) in developers) {
println("$author made $language")
}
println("${developers["Kotlin"]} rocks")
}

53. Collections
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }
.map { "${it.firstName} ${it.lastName}” }

54. Collections
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }
.map { "${it.firstName} ${it.lastName}” }

55. Collections
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }
.map { "${it.firstName} ${it.lastName}” }

56. Collections
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }
.map { "${it.firstName} ${it.lastName}” }

57. Inline Functions
public inline fun <T>
Iterable<T>.filter(
predicate: (T) -> Boolean): List<T>
{
val destination = ArrayList<T>()
for (element in this) {
if (predicate(element))
destination.add(element)
}
return destination
}

58. Inline Functions
public inline fun <T>
Iterable<T>.filter(
predicate: (T) -> Boolean): List<T>
{
val destination = ArrayList<T>()
for (element in this) {
if (predicate(element))
destination.add(element)
}
return destination
}

59. Inline Functions
public inline fun <T>
Iterable<T>.filter(
predicate: (T) -> Boolean): List<T>
{
val destination = ArrayList<T>()
for (element in this) {
if (predicate(element))
destination.add(element)
}
return destination
}

60. Function References
fun nobles(persons: List<Person>)
= persons.filter(::isNoble)
fun isNoble(person: Person)
= person.lastName.startsWith("von ") ||
person.lastName.startsWith("zu ")

61. Member Extensions
class Person(val firstName: String,
val lastName: String) {
fun isNoble() = lastName.hasNoblePrefix()
fun String.hasNoblePrefix()
= startsWith("von ") ||
startsWith("zu ")
}

62. Reified Type Parameters
inline fun <reified T>
TreeNode.findParentOfType(): T? {
var p = parent
while (p != null && p !is T) {
p = p?.parent
}
return p as T
}
fun findDirectory(node: TreeNode)
= node.findParentOfType<DirectoryNode>()

63. Reified Type Parameters
inline fun <reified T>
TreeNode.findParentOfType(): T? {
var p = parent
while (p != null && p !is T) {
p = p?.parent
}
return p as T
}
fun findDirectory(node: TreeNode)
= node.findParentOfType<DirectoryNode>()

64. Reified Type Parameters
inline fun <reified T>
TreeNode.findParentOfType(): T? {
var p = parent
while (p != null && p !is T) {
p = p?.parent
}
return p as T
}
fun findDirectory(node: TreeNode)
= node.findParentOfType<DirectoryNode>()

65. Reified Type Parameters
inline fun <reified T>
TreeNode.findParentOfType(): T? {
var p = parent
while (p != null && p !is T) {
p = p?.parent
}
return p as T
}
fun findDirectory(node: TreeNode)
= node.findParentOfType<DirectoryNode>()

66. HTML Builders
h1 {
+"No Users"
}
p {
+"No users found. Please make sure "
a {
href = TeamRoute("invitations", team)
+"invitation codes"
}
+" are available to eligible users."
}

67. HTML Builders
h1 {
+"No Users"
}
p {
+"No users found. Please make sure "
a {
href = TeamRoute("invitations", team)
+"invitation codes"
}
+" are available to eligible users."
}

68. HTML Builders
h1 {
+"No Users"
}
p {
+"No users found. Please make sure "
a {
href = TeamRoute("invitations", team)
+"invitation codes"
}
+" are available to eligible users."
}

69. Kotlin Tooling

70. Kotlin Tooling
• IntelliJ plugin since day 0

71. Kotlin Tooling
• IntelliJ plugin since day 0
• Eclipse plugin just reached alpha

72. Kotlin Tooling
• IntelliJ plugin since day 0
• Eclipse plugin just reached alpha
• Ant, Maven, Gradle plugins

73. Kotlin for Android

74. Kotlin for Android
• Compiler extension to inject views

75. Kotlin for Android
• Compiler extension to inject views
• Builder DSL to construct user interfaces

76. Kotlin for Android
• Compiler extension to inject views
• Builder DSL to construct user interfaces
• Fully compatible with Android Studio

77. Status of Kotlin

78. Status of Kotlin
• Compiler and IntelliJ IDEA plugin stable and
production-ready

79. Status of Kotlin
• Compiler and IntelliJ IDEA plugin stable and
production-ready
• Finalizing design of language and standard library

80. Status of Kotlin
• Compiler and IntelliJ IDEA plugin stable and
production-ready
• Finalizing design of language and standard library
• Expecting 1.0 release later this year

81. Summary

82. Summary
• Kotlin is safe, concise and expressive

83. Summary
• Kotlin is safe, concise and expressive
• Kotlin can be gradually introduced in any existing
Java project

84. Summary
• Kotlin is safe, concise and expressive
• Kotlin can be gradually introduced in any existing
Java project
• Kotlin is stable and ready for production use

85. Q&A
http://kotlinlang.org/
@intelliyole
yole@jetbrains.com