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Kotlin: Write Once, Run Actually Everywhere (QC...

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

Jake Wharton

November 06, 2018
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  1. class User {
 public String getName() {
 // ...
 }


    public void setName(String name) {
 // ...
 }
 } // ^^^ Java
  2. class User {
 public String getName() {
 // ...
 }X


    public void setName(String name) {
 // ...
 }Y
 }Z // ^^^ Java vvv Kotlin val user = User()
 println("Name is " + user.name)
  3. 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
  4. 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
  5. class User {
 public String getName() {
 // ...
 }X


    public void setName(String name) {
 // ...
 }Y
 }Z // ^^^ Java vvv Kotlin val user = User()
 println("Name is $user")X
  6. class User {
 public String getName() {
 // ...
 }X


    public void setName(String name) {
 // ...
 }Y
 }Z // ^^^ Java vvv Kotlin val user = User()
 println("Name is $user")X
  7. class User {
 var name = "Jake"
 } // ^^^

    Kotlin vvv Java User user = new User(); System.out.println("Name is " + user.getName());
  8. class User {
 var name = "Jake"
 } // ^^^

    Kotlin vvv Java User user = new User(); System.out.println("Name is " + user.getName());
  9. class User {
 var name = "Jake"
 } // ^^^

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

    Kotlin vvv Java User user = new User(); System.out.println("Name is " + user.getName()); user.setName("Jane");
  11. 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.")
 }
  12. 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.")
 }
  13. 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)
  14. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter({ item -> item % 2 != 0 })B
  15. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter({ item -> item % 2 != 0 })B
  16. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter({ it % 2 != 0 })B
  17. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter()B{ it % 2 != 0 }
  18. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter { it % 2 != 0 }
  19. 
 
 val odds fun <T> List<T>.filter(predicate: (T) -> Boolean):

    List<T> {
 // ...
 }A val items = listOf(1, 2, 3) List = items.filter { it % 2 != 0 } val oddSet = items.filterTo(mutableListOf()) { it % 2 != 0 }
  20. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...


    }A val items = listOf(1, 2, 3) val odds = items.filter { it % 2 != 0 }
  21. inline fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 //

    ...
 }A val items = listOf(1, 2, 3) val odds = items.filter { it % 2 != 0 }
  22. inline fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { val

    destination = mutableListOf<T>() 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
  23. inline fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> { val

    destination = mutableListOf<T>() for (item in this) { if (predicate(item)) destination.add(item) }B return destination }A val items = listOf(1, 2, 3) val destination = mutableListOf<Int>() for (item in items) { if (item % 2 != 0) destination.add(item) }G val odds = destination filter it
  24. @3a71f4dd data class User(val name: String) val jake = User("Jake")

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

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

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

    = User("Jake", 4) val (name, age) = dbLookup()
  28. class UserPersisence(db: SqlDatabase) { private val deleteByName = db.createStatement("DELETE FROM

    user WHERE name = ?") fun delete(name: String) { deleteByName.bind(1, name) deleteByName.execute() } }
  29. 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
  30. 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
  31. 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") }
  32. 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<String>()
  33. 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<String>() val nameView by bindView<TextView>(R.id.name)
  34. 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<String>() val nameView by bindView<TextView>(R.id.name)
  35. fun main(vararg args: String) = runBlocking<Unit> { val jobs =

    List(100_000) { launch(CommonPool) { delay(1000L) print(".") } } jobs.forEach { it.join() } }
  36. 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);
  37. 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(); }
  38. 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)
  39. 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
  40. 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
  41. class NewGamePresenter(private val gameStore: GameStore) {C fun model(): NewGameUiModel {

    val totals = gameStore.totals() return NewGameUiModel(totals.wins, totals.losses) }B }A
  42. class GamePresenter( private val gameId: Long, private val gameStore: GameStore

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

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

    ) {D fun models(events: Observable<UiEvent>): Observable<GameUiModel> {C }B sealed class UiEvent { data class Move(val row: Int, val col: Int): UiEvent() // ... } }A fun move( )Z{C }G
  45. interface GameStore { suspend fun totals(): Totals fun game(id: Long):

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

    Observable<Game> suspend fun move(id: Long, row: Int, col: Int) data class Totals(val wins: Long, val losses: Long) }A
  47. Android iOS Web iOS Web Server / API Android View

    Models Presenters Client Backend Business Logic Models
  48. 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() }
  49. 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() }
  50. 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
  51. 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
  52. 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
  53. 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
  54. Android iOS Web iOS Web Server / API Android View

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

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

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

    Models Presenters Client Backend Business Logic Models
  58. 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() }
  59. Android iOS Web iOS Web Server / API Android View

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

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

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

    Models Presenters Client Backend Business Logic Models
  63. class GameView(context: Context, attrs: AttributeSet) : ContraintLayout(context, attrs), Consumer<GamePresenter.UiModel> {

    override fun accept(model: GamePresenter.UiModel) { // TODO bind to view... } }
  64. @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 ... }
  65. 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
  66. external interface ChromePlatform { val omnibox: Omnibox val storage: Storage

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

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

    val tabs: Tabs }A @JsName("chrome") external val Chrome: ChromePlatform
  69. 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) // ... }
  70. 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() }
  71. 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() }
  72. 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
  73. 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
  74. 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
  75. import kotlin.collections.MutableList val users: MutableList<String> = CopyOnWriteArrayList() expect class CopyOnWriteArrayList<T>

    : MutableList<T> actual typealias CopyOnWriteArrayList<T> = java.util.concurrent.CopyOnWriteArrayList<T>
  76. import kotlin.collections.MutableList val users: MutableList<String> = CopyOnWriteArrayList() expect class CopyOnWriteArrayList<T>

    : MutableList<T> actual typealias CopyOnWriteArrayList<T> = java.util.concurrent.CopyOnWriteArrayList<T> actual typealias CopyOnWriteArrayList<T> = ArrayList<T>
  77. import kotlin.collections.MutableList val users: MutableList<String> = CopyOnWriteArrayList() expect class CopyOnWriteArrayList<T>

    : MutableList<T> actual typealias CopyOnWriteArrayList<T> = java.util.concurrent.CopyOnWriteArrayList<T> actual typealias CopyOnWriteArrayList<T> = ArrayList<T> actual class CopyOnWriteArrayList<T> : MutableList<T> { // it's complicated... }
  78. expect interface Closeable { fun close() } actual typealias Closeable

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