Kotlin: Write Once, Run Actually Everywhere (QCon SF 2018)

Kotlin used to be described as a new language for the JVM which aims to fix some of the pain points of Java. But more recently Kotlin is also a language for the web, iOS, desktop, embedded, and just about anywhere else code can run. JetBrains, the creators of Kotlin, have placed a strong emphasis on targeting multiple platforms in how the language is compiled, its language features, and the standard libraries. This talk will be an exploration of the Kotlin language, how it compiles to run on more than just the JVM, and whether it can fully pull off the multiplatform trick allowing a single codebase to run everywhere.

Video: coming soon

Transcript

1. Jake Wharton
   Kotlin: Write Once,
   Run Everywhere
   Actually
   

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2. Kotlin?
   

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8. val firstName: String = "Jake"

   val lastName: String? = null
   

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9. val firstName: String = "Jake"

   val lastName: String? = null
   

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10. val firstName: String = "Jake"

    val lastName: String? = null
    

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11. val firstName: String = "Jake"

    val lastName: String? = null
    

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12. val firstName: String = "Jake"

    val lastName: String? = null
    

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13. val firstName = "Jake"

    val lastName: String? = null
    

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14. class User {

    public String getName() {

    // ...

    }

    public void setName(String name) {

    // ...

    }

    }
    // ^^^ Java
    

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15. class User {

    public String getName() {

    // ...

    }X

    public void setName(String name) {

    // ...

    }Y

    }Z
    // ^^^ Java vvv Kotlin
    val user = User()

    println("Name is " + user.name)
    

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16. class User {

    public String getName() {

    // ...

    }X

    public void setName(String name) {

    // ...

    }Y

    }Z
    // ^^^ Java vvv Kotlin
    val user = User()

    println("Name is " + user.name)X
    

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17. class User {

    public String getName() {

    // ...

    }X

    public void setName(String name) {

    // ...

    }Y

    }Z
    // ^^^ Java vvv Kotlin
    val user = User()

    println("Name is ${user.name}")X
    

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18. class User {

    public String getName() {

    // ...

    }X

    public void setName(String name) {

    // ...

    }Y

    }Z
    // ^^^ Java vvv Kotlin
    val user = User()

    println("Name is $user")X
    

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19. class User {

    public String getName() {

    // ...

    }X

    public void setName(String name) {

    // ...

    }Y

    }Z
    // ^^^ Java vvv Kotlin
    val user = User()

    println("Name is $user")X
    

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20. class User {

    var name = "Jake"

    }
    // ^^^ Kotlin
    

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21. class User {

    var name = "Jake"

    }
    // ^^^ Kotlin vvv Java
    User user = new User();
    System.out.println("Name is " + user.getName());
    

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22. class User {

    var name = "Jake"

    }
    // ^^^ Kotlin vvv Java
    User user = new User();
    System.out.println("Name is " + user.getName());
    

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23. class User {

    var name = "Jake"

    }
    // ^^^ Kotlin vvv Java
    User user = new User();
    System.out.println("Name is " + user.getName());
    user.setName("Jane");
    

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24. class User {

    var name = "Jake"

    }
    // ^^^ Kotlin vvv Java
    User user = new User();
    System.out.println("Name is " + user.getName());
    user.setName("Jane");
    

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25. val user = User()
    

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26. val user = User()

    user = User()
    

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27. val user = User()

    user = User()

    

    var currentUser = User()

    currentUser = User()
    

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28. fun Date.isTuesday(): Boolean {

    return day == 2

    }
    

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29. fun Date.isTuesday(): Boolean {

    return day == 2

    }
    val epoch = Date(1970, 0, 0)

    if (epoch.isTuesday()) {

    println("The epoch was a Tuesday.")

    } else {

    println("The epoch was not a Tuesday.")

    }
    

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30. fun Date.isTuesday(): Boolean {

    return day == 2

    }
    val epoch = Date(1970, 0, 0)

    if (epoch.isTuesday()) {

    println("The epoch was a Tuesday.")

    } else {

    println("The epoch was not a Tuesday.")

    }
    

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31. fun Date.isTuesday(): Boolean {

    return day == 2

    }
    val epoch = Date(1970, 0, 0)

    if (epoch.isTuesday()) {

    println("The epoch was a Tuesday.")

    } else {

    println("The epoch was not a Tuesday.")

    }
    // ^^^ Kotlin vvv Java
    DateKt.isTuesday(date)
    

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32. val executor = Executors.newSingleThreadExecutor();

    executor.execute {Bprintln("Background thread!") }X
    

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33. val executor = Executors.newSingleThreadExecutor();
    val foo = Foo()

    executor.execute(foo::printIt)
    class Foo {
    fun printIt() {B
    println("Background thread!")
    }X
    }
    

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34. val executor = Executors.newSingleThreadExecutor();
    val foo = Foo()

    executor.execute(foo::printIt)
    class Foo {
    fun printIt() {B
    println("Background thread!")
    }X
    }
    

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35. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }
    

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36. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }
    

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37. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter({ item -> item % 2 != 0 })B
    

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38. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter({ item -> item % 2 != 0 })B
    

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39. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter({ it % 2 != 0 })B
    

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40. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter()B{ it % 2 != 0 }
    

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41. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter { it % 2 != 0 }
    

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42. 

    

    val odds
    fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    List = items.filter { it % 2 != 0 }
    val oddSet = items.filterTo(mutableListOf()) { it % 2 != 0 }
    

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43. fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter { it % 2 != 0 }
    

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44. inline fun List.filter(predicate: (T) -> Boolean): List {

    // ...

    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter { it % 2 != 0 }
    

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45. inline fun List.filter(predicate: (T) -> Boolean): List {
    val destination = mutableListOf()
    for (item in this) {
    if (predicate(item)) destination.add(item)
    }B
    return destination
    }A
    val items = listOf(1, 2, 3)
    val odds = items.filter { it % 2 != 0 }
    val destination = mutableListOf< >()
    for (item in ) {
    if ( item ) destination.add(item)
    }G
    destination
    

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46. inline fun List.filter(predicate: (T) -> Boolean): List {
    val destination = mutableListOf()
    for (item in this) {
    if (predicate(item)) destination.add(item)
    }B
    return destination
    }A
    val items = listOf(1, 2, 3)
    val destination = mutableListOf()
    for (item in items) {
    if (item % 2 != 0) destination.add(item)
    }G
    val odds = destination
    filter it
    

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47. class User {D

    val name = "Jake"

    }A
    

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48. class User(name: String) {D

    val name = name

    }A
    

    "Jake"
    

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49. class User(val name: String) {

    }A
    

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50. class User(val name: String)
    

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51. class User(val name: String)
    val jake = User("Jake")
    println("Hello, $jake!")
    

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52. class User(val name: String)
    val jake = User("Jake")
    println("Hello, $jake!")
    Hello, User@3a71f4dd!
    

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53. data class User(val name: String)
    val jake = User("Jake")
    println("Hello, $jake!")
    Hello, User@3a71f4dd!
    

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54. @3a71f4dd
    data class User(val name: String)
    val jake = User("Jake")
    println("Hello, $jake!")
    Hello, User(name=Jake)!
    

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55. data class User(val name: String)
    val jake = User("Jake")
    println("Hello, $jake!")
    Hello, User(name=Jake)!
    

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56. data class User(val name: String, val age: Int)
    val jake = User("Jake")
    println("Hello, $jake!")
    Hello, User(name=Jake)!
    

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57. data class User(val name: String, val age: Int)
    val jake = User("Jake", 4)
    

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58. data class User(val name: String, val age: Int)
    val jake = User("Jake", 4)
    val (name, age) = jake
    

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59. data class User(val name: String, val age: Int)
    val (name, age) = User("Jake", 4)
    

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60. data class User(val name: String, val age: Int)
    fun dbLookup() = User("Jake", 4)
    val (name, age) = dbLookup()
    

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61. class UserPersisence(db: SqlDatabase) {
    private val deleteByName
    = db.createStatement("DELETE FROM user WHERE name = ?")
    fun delete(name: String) {
    deleteByName.bind(1, name)
    deleteByName.execute()
    }
    }
    

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62. class UserPersisence(db: SqlDatabase) {
    private val deleteByName
    = db.createStatement("DELETE FROM user WHERE name = ?")
    fun delete(name: String) {
    deleteByName.bind(1, name)
    deleteByName.execute()
    }B
    }A
    

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63. class UserPersisence(db: SqlDatabase) {
    private val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    fun delete(name: String) {
    deleteByName.bind(1, name)
    deleteByName.execute()
    }B
    }A
    

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64. val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    

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65. val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    var name by Delegates.observable("Jane") { prop, old, new ->
    println("Name changed from $old to $new")
    }
    

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66. val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    var name by Delegates.observable("Jane") { prop, old, new ->
    println("Name changed from $old to $new")
    }
    var address by Delegates.notNull()
    

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67. val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    var name by Delegates.observable("Jane") { prop, old, new ->
    println("Name changed from $old to $new")
    }
    var address by Delegates.notNull()
    val nameView by bindView(R.id.name)
    

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68. val deleteByName by lazy {
    db.createStatement("DELETE FROM user WHERE name = ?")
    }C
    var name by Delegates.observable("Jane") { prop, old, new ->
    println("Name changed from $old to $new")
    }
    var address by Delegates.notNull()
    val nameView by bindView(R.id.name)
    

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69. fun main(vararg args: String) = runBlocking {
    val jobs = List(100_000) {
    launch(CommonPool) {
    delay(1000L)
    print(".")
    }
    }
    jobs.forEach { it.join() }
    }
    

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73. Multiplatform Abstraction Your App
    

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74. Your App
    

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75. Your App
    

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76. X O X
    X X O
    O O X
    

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77. iOS Web Server / API
    Android
    

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78. Android
    

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79. package xo;
    public enum Mark {
    X, O;
    }
    

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80. package xo;
    import java.util.Arrays;
    public final class Board {
    private static final int SIZE = 3;
    private final Mark[][] cells;
    public Board() {
    this.cells = new Mark[3][3];
    }
    // TODO mutator methods...
    @Override public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Board)) return false;
    Board other = (Board) o;
    return Arrays.deepEquals(cells, other.cells);
    }
    @Override public int hashCode() {
    return Arrays.deepHashCode(cells);
    

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81. package xo;
    import static java.util.Objects.requireNonNull;
    public final class Player {
    public final String name;
    public final Mark mark;
    public Player(String name, Mark mark) {
    this.name = requireNonNull(name, "name == null");
    this.mark = requireNonNull(mark, "mark == null");
    }
    @Override public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Player)) return false;
    Player other = (Player) o;
    return name.equals(other.name) && mark == other.mark;
    }
    @Override public int hashCode() {
    return 31 * name.hashCode() + mark.hashCode();
    }
    

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82. package xo;
    public enum State {
    PLAYER_1_MOVE,
    PLAYER_2_MOVE,
    PLAYER_1_WIN,
    PLAYER_2_WIN,
    DRAW,
    }
    

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83. package xo;
    import static java.util.Objects.requireNonNull;
    public final class Game {
    private final Board board;
    private final Player player1;
    private final Player player2;
    private State state = State.PLAYER_1_MOVE;
    public Game(Board board, Player player1, Player player2) {
    this.board = requireNonNull(board, "board == null");
    this.player1 = requireNonNull(player1, "player1 == null");
    this.player2 = requireNonNull(player2, "player2 == null");
    }
    // TODO mutator methods...
    @Override public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Game)) return false;
    Game other = (Game) o;
    return board.equals(other.board)
    && player1.equals(other.player1)
    

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84. Game Board Mark
    State
    Player
    

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85. Game Board Mark
    State
    Player
    

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86. public final class Player {
    public final String name;
    public final Mark mark;
    public Player(String name, Mark mark) {
    this.name = requireNonNull(name, "name == null");
    this.mark = requireNonNull(mark, "mark == null");
    }A
    @Override public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Player)) return false;
    Player other = (Player) o;
    return name.equals(other.name) && mark == other.mark;
    }B
    @Override public int hashCode() {
    return 31 * name.hashCode() + mark.hashCode();
    }C
    @Override public String toString() {
    return "Player{name='" + name + ", mark=" + mark + '}';
    }D
    }E
    

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87. data class Player(val name: String, val mark: Mark)
    public final {
    public final ;
    public final ;
    public Player(String name, Mark mark) {
    this.name = requireNonNull(name, "name == null");
    this.mark = requireNonNull(mark, "mark == null");
    }A
    @Override public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Player)) return false;
    Player other = (Player) o;
    return name.equals(other.name) && mark == other.mark;
    }B
    @Override public int hashCode() {
    return 31 * name.hashCode() + mark.hashCode();
    }C
    @Override public String toString() {
    return "Player{name='" + name + ", mark=" + mark + '}';
    }D
    }E
    

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88. Game Mark
    State
    Board
    Player
    

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89. State
    Board
    Game Mark
    Player
    

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90. Game Mark
    State
    Board
    *.java
    *.kt
    Player
    

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91. *.kt
    Game
    Mark
    State
    *.java
    

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92. kotlinc
    *.kt
    Game
    Mark
    State
    *.java
    

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93. *.kt
    Game
    Mark
    State
    *.java
    kotlinc
    

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94. javac
    *.kt
    Game
    Mark
    State
    *.java
    kotlinc
    

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95. kotlinc javac
    *.kt
    Game
    Mark
    State
    *.java
    

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96. kotlinc javac
    *.kt
    Game
    Mark
    State
    *.java
    

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97. kotlin-stdlib
    kotlinc javac
    *.kt
    Game
    Mark
    State
    *.java
    

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98. kotlin-stdlib
    kotlinc javac
    *.kt
    Game
    Mark
    State
    *.java
    models/
    

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99. iOS Web Server / API
    Android
    

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100. iOS Web Server / API
     Android
     

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101. iOS
     Web Server / API
     Android
     View Models
     

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102. iOS
     Web Server / API
     Android
     View Models
     Presenters
     

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103. iOS
     Web Server / API
     Android
     View Models
     Presenters
     

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104. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     

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105. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     

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106. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     

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107. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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108. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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109. data class NewGameUiModel(
     val winTotal: Long,
     val lossTotal: Long
     )
     

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110. data class NewGameUiModel(
     val winTotal: Long,
     val lossTotal: Long
     )
     data class GameUiModel(
     val game: Game
     )
     

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111. data class NewGameUiModel(
     val winTotal: Long,
     val lossTotal: Long
     )
     data class GameUiModel(
     )
     val game: Game
     

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112. data class NewGameUiModel(
     val winTotal: Long,
     val lossTotal: Long
     )
     data class GameUiModel(
     val game: Game
     )
     

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113. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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114. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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115. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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116. class NewGamePresenter {C
     fun model(): NewGameUiModel {
     }B
     }A
     

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117. class NewGamePresenter(private val gameStore: GameStore) {C
     fun model(): NewGameUiModel {
     }B
     }A
     

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118. class NewGamePresenter(private val gameStore: GameStore) {C
     fun model(): NewGameUiModel {
     val totals = gameStore.totals()
     return NewGameUiModel(totals.wins, totals.losses)
     }B
     }A
     

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119. class GamePresenter {D
     fun model(): GameUiModel {C
     }B
     }A
     

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120. class GamePresenter(private val gameId: Long) {D
     fun model(): GameUiModel {C
     }B
     }A
     

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121. class GamePresenter(
     private val gameId: Long,
     private val gameStore: GameStore
     ) {D
     fun model(): GameUiModel {C
     }B
     }A
     

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122. class GamePresenter(
     private val gameId: Long,
     private val gameStore: GameStore
     ) {D
     fun models(): Observable {C
     }B
     }A
     

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123. class GamePresenter(
     private val gameId: Long,
     private val gameStore: GameStore
     ) {D
     fun move(row: Int, col: Int )Z{C
     }G
     fun models(): Observable {C
     }B
     }A
     

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124. class GamePresenter(
     private val gameId: Long,
     private val gameStore: GameStore
     ) {D
     fun models(events: Observable): Observable {C
     }B
     sealed class UiEvent {
     data class Move(val row: Int, val col: Int): UiEvent()
     // ...
     }
     }A
     fun move( )Z{C
     }G
     

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125. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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126. iOS
     Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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127. iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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128. iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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129. interface GameStore {
     }A
     

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130. interface GameStore {
     suspend fun totals(): Totals
     data class Totals(val wins: Long, val losses: Long)
     }A
     

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131. interface GameStore {
     suspend fun totals(): Totals
     fun game(id: Long): Observable
     data class Totals(val wins: Long, val losses: Long)
     }A
     

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132. interface GameStore {
     suspend fun totals(): Totals
     fun game(id: Long): Observable
     suspend fun move(id: Long, row: Int, col: Int)
     data class Totals(val wins: Long, val losses: Long)
     }A
     

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133. iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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134. iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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135. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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136. class SqliteGameStore(private val db: SQLiteDatabase) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     

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137. class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     

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138. class IosGameStore( ) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     private val db: CoreDataGameStore
     

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139. class IosGameStore( ) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     private val db: CoreDataGameStore
     // tictactoe.def
     headers = game_store.h
     

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140. class StorageGameStore(private val store: Storage) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }A
     

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141. import org.w3c.dom.Storage
     class StorageGameStore( ) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }A
     private val store: Storage
     

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142. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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143. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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144. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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145. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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146. object TicTacToeLogic {
     fun validateMove(
     game: Game, player: Player, row: Int, col: Int): Boolean {
     when (game.state) {
     State.PLAYER_1_MOVE -> require(game.player1 == player)
     State.PLAYER_2_MOVE -> require(game.player2 == player)
     else -> error("Game is over")
     }
     return game.board[row][col] == null
     }
     fun nextState(game: Game): State {
     findWinner(game.board)?.let {
     return if (game.player1.mark == it) State.PLAYER_1_WIN
     else State.PLAYER_2_WIN
     }
     if (game.board.isComplete()) {
     return State.DRAW
     }
     return if (game.state == State.PLAYER_1_MOVE) State.PLAYER_2_MOVE
     else State.PLAYER_1_MOVE
     }
     fun findWinner(board: Board): Mark? = TODO()
     fun Board.isComplete(): Boolean = TODO()
     }
     

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147. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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148. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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149. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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150. Android iOS Web
     iOS Web
     Server / API
     Android
     View Models
     Presenters
     Client Backend
     Business Logic
     Models
     

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151. class GameView(context: Context, attrs: AttributeSet)
     : ContraintLayout(context, attrs),
     Consumer {
     override fun accept(model: GamePresenter.UiModel) {
     // TODO bind to view...
     }
     }
     

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152. class GameViewController : UiViewController {
     func update(model: GamePresenter.UiModel) {
     // TODO bind to view...
     }
     }
     

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153. function update(model) {
     // TODO bind to DOM/template/JSX/whatever...
     }
     

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154. @POST @Path("/api/move")
     fun Game move(
     @QueryParam("id") id: Long,
     @QueryParam("row") row: Int,
     @QueryParam("col") col: Int) {
     // TODO check business logic, persist, return updated game ...
     }
     

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155. View Slide

156. apk via aab
     apk
     via
     aab
     apk
     webapk
     apk via aab
     via url
     url
     apk via aab
     via url
     Chrome app
     url
     url
     pwa
     ipa
     ipa
     url
     url
     

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157. View Slide

158. View Slide

159. kotlin-stdlib
     kotlinc javac
     *.kt
     *.java
     

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160. View Slide

161. View Slide

162. external interface ChromePlatform {
     val omnibox: Omnibox
     val storage: Storage
     val tabs: Tabs
     }A
     @JsName("chrome")
     external val Chrome: ChromePlatform
     

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163. $ ts2kt chrome.ts
     external interface ChromePlatform {
     val omnibox: Omnibox
     val storage: Storage
     val tabs: Tabs
     }A
     @JsName("chrome")
     external val Chrome: ChromePlatform
     

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164. external interface ChromePlatform {
     val omnibox: Omnibox
     val storage: Storage
     val tabs: Tabs
     }A
     @JsName("chrome")
     external val Chrome: ChromePlatform
     

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165. external interface ChromePlatform {
     val omnibox: Omnibox
     val storage: Storage
     val tabs: Tabs
     }A
     @JsName("chrome")
     external val Chrome: ChromePlatform
     fun main(vararg args: String) {
     val configStore = StorageAreaConfigStore(
     Chrome.storage.sync, PRODUCTION_GIT_WEB, PRODUCTION_DAC)
     // ...
     }
     

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166. function main(args) {
     var configStore = new StorageAreaConfigStore(chrome.storage.sync,
     reference.PRODUCTION_GIT_WEB, reference.PRODUCTION_DAC);
     // ...
     }
     

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167. View Slide

168. View Slide

169. class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     

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170. class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     

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171. class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }
     // tictactoe.def
     headers = game_store.h
     

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172. class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }A
     // tictactoe.def
     headers = game_store.h
     package = gamestore
     

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173. import gamestore.CoreDataGameStore
     class IosGameStore(private val db: CoreDataGameStore) : GameStore {
     override suspend fun totals() = TODO()
     override fun game(id: Long) = TODO()
     override suspend fun move(id: Long, row: Int, col: Int) = TODO()
     }A
     // tictactoe.def
     headers = game_store.h
     package = gamestore
     

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174. konan
     *.kt
     

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175. konan
     *.kt
     *.h
     

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176. konan
     *.kt
     llvm
     *.h
     

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177. konan
     *.kt
     llvm
     *.h
     

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178. konan
     *.kt
     llvm
     *.h
     

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179. View Slide

180. View Slide

181. import kotlin.collections.ArrayList
     import kotlin.collections.MutableList
     val users: MutableList = ArrayList()
     

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182. import java.util.concurrent.CopyOnWriteList
     import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     kotlin.collections.ArrayList
     

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183. import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     

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184. import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     expect class CopyOnWriteArrayList : MutableList
     

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185. import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     expect class CopyOnWriteArrayList : MutableList
     actual typealias CopyOnWriteArrayList =
     java.util.concurrent.CopyOnWriteArrayList
     

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186. import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     expect class CopyOnWriteArrayList : MutableList
     actual typealias CopyOnWriteArrayList =
     java.util.concurrent.CopyOnWriteArrayList
     actual typealias CopyOnWriteArrayList = ArrayList
     

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187. import kotlin.collections.MutableList
     val users: MutableList = CopyOnWriteArrayList()
     expect class CopyOnWriteArrayList : MutableList
     actual typealias CopyOnWriteArrayList =
     java.util.concurrent.CopyOnWriteArrayList
     actual typealias CopyOnWriteArrayList = ArrayList
     actual class CopyOnWriteArrayList : MutableList {
     // it's complicated...
     }
     

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188. expect interface Closeable {
     fun close()
     }
     

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189. expect interface Closeable {
     fun close()
     }
     actual typealias Closeable = java.io.Closeable
     actual interface Closeable {
     actual fun close()
     }
     actual interface Closeable {
     actual fun close()
     }
     

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190. View Slide

191. View Slide

192. SDK Search
     

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193. View Slide

194. View Slide

195. View Slide

196. View Slide

197. @JakeWharton
     Kotlin: Write Once,
     Run Everywhere
     Actually
     

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