Kotlin: Uncovered

Kotlin does a lot for us in the way of reducing boilerplate. But what is it really doing? We will be inspecting some decompiled Kotlin to discover how it does its job. By looking underneath at how it handles data classes, lambdas, and delegation, we can better understand how the language executes what we write. If you’re curious about the language, or already using it in production, you should walk away from this investigation with a deeper understanding of Kotlin, and some tools for continued exploration.

- As given at Droidcon Boston '17 and Chicago Roboto '17

Transcript

1. @TTGonda
   collectiveidea.com
   Kotlin: Uncovered
   Victoria Gonda
   www.victoriagonda.com
   @TTGonda
   

   View Slide

2. @TTGonda
   collectiveidea.com
   Holland, MI
   Dancer
   Collective Idea
   

   View Slide

3. @TTGonda
   collectiveidea.com
   I ❤
   Programming
   Languages
   

   View Slide

4. @TTGonda
   collectiveidea.com
   DEFINE('BUBBLE(A,ALEN)I,J,UB,TMP') :
   (BUBBLE_END)
   BUBBLE I = 1; UB = ALEN
   OUTER GT(UB,1) :F(BDONE)
   J = 1
   INNER LE(A, A) :S(INCRJ)
   TMP = A
   A = A
   A = TMP
   INCRJ J = LT(J + 1,UB) J + 1 :S(INNER)
   UB = UB - 1 :(OUTER)
   BDONE BUBBLE = A :(RETURN)
   BUBBLE_END
   NUMBERS = '33 99 15 54 1 20 88 47 68 72'
   OUTPUT = "Unsorted List"
   OUTPUT = NUMBERS;
   NUMARRAY = ARRAY(10)
   FLOOP I = I + 1
   NUMBERS SPAN('0123456789') . NUMARRAY =
   :S(FLOOP)
   BUBBLE(NUMARRAY,10); NUMBERS = ''
   SLOOP J = J + 1;
   NUMBERS = NUMBERS NUMARRAY '
   ' :S(SLOOP)
   OUTPUT = TRIM(NUMBERS)
   END
   SNOBOL
   

   View Slide

5. @TTGonda
   collectiveidea.com
   HAI 1.2
   CAN HAS STDIO?
   VISIBLE "IS KITTAH GAME!"
   VISIBLE "ENTER 'HELP' FOR CONTROLS"
   VISIBLE ""
   I HAS A NAME
   VISIBLE "WHAT IS KITTAH'S NAME?"
   GIMMEH NAME
   I HAS A ACTION
   VISIBLE SMOOSH "WAT U WANTING TO DO WITH " NAME "?" MKAY
   GIMMEH ACTION
   IM IN YR LOOP NERFIN YR PURRS TIL BOTH SAEM ACTION AN "KBYE"
   BOTH SAEM ACTION AN "HELP", O RLY?
   YA RLY
   VISIBLE "PET"
   VISIBLE "FEED"
   VISIBLE "IS HAPPY?"
   VISIBLE "KBYE"
   MEBBE BOTH SAEM ACTION AN "PURRS"
   VISIBLE SMOOSH "PURRS: " PURRS MKAY
   MEBBE BOTH SAEM ACTION AN "FEED"
   VISIBLE SMOOSH "YOU DID FEED " NAME ". " NAME " IS HAPPY WITH FOOD." MKAY
   PURRS R SUM OF PURRS AN 3
   LOLCODE
   

   View Slide

6. @TTGonda
   collectiveidea.com
   

   View Slide

7. @TTGonda
   collectiveidea.com
   “Statically typed programming language
   for the JVM, Android and the browser”
   

   View Slide

8. @TTGonda
   collectiveidea.com
   Statically Typed
   

   View Slide

9. @TTGonda
   collectiveidea.com
   Statically Typed
   final String name = "Victoria";
   val name = "Victoria"
   

   View Slide

10. @TTGonda
    collectiveidea.com
    Null Safety
    

    View Slide

11. @TTGonda
    collectiveidea.com
    Null Safety
    NullPointerException
    

    View Slide

12. @TTGonda
    collectiveidea.com
    Concise
    

    View Slide

13. @TTGonda
    collectiveidea.com
    map{$P=$P[$f^ord($p{$_})&6];$p{$_}=/ ^$P/ix?$P:close$_}
    Perl
    

    View Slide

14. @TTGonda
    collectiveidea.com
    

    View Slide

15. @TTGonda
    collectiveidea.com
    Java Virtual Machine
    

    View Slide

16. @TTGonda
    collectiveidea.com
    Java Virtual Machine
    

    View Slide

17. @TTGonda
    collectiveidea.com
    

    View Slide

18. @TTGonda
    collectiveidea.com
    

    View Slide

19. @TTGonda
    collectiveidea.com
    Data Classes
    Null Safety
    Delegation
    Class Extensions
    Lambdas
    

    View Slide

20. @TTGonda
    collectiveidea.com
    Data Classes
    

    View Slide

21. @TTGonda
    collectiveidea.com
    class User(
    val firstName: String,
    var lastName: String?
    )
    
    

    View Slide

22. @TTGonda
    collectiveidea.com
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private String lastName;
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    @NotNull
    public final String getFirstName() {
    return this.firstName;
    }
    @Nullable
    public final String getLastName() {
    return this.lastName;
    }
    public final void setLastName(@Nullable String var1) {
    this.lastName = var1;
    }
    }
    
    

    View Slide

23. @TTGonda
    collectiveidea.com
    public final class User {
    
    

    View Slide

24. @TTGonda
    collectiveidea.com
    @NotNull
    private final String firstName;
    @Nullable
    private String lastName;
    public final class User {
    
    

    View Slide

25. @TTGonda
    collectiveidea.com
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private final String lastName;
    
    

    View Slide

26. @TTGonda
    collectiveidea.com
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private final String lastName;
    
    public static void checkParameterIsNotNull(
    Object value, String paramName) {
    if (value == null) {
    // prints error with stack trace
    throwParameterIsNullException(paramName);
    }
    }
    

    View Slide

27. @TTGonda
    collectiveidea.com
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private final String lastName;
    
    public static void checkParameterIsNotNull(
    Object value, String paramName) {
    if (value == null) {
    // prints error with stack trace
    throwParameterIsNullException(paramName);
    }
    }
    Caused by:
    java.lang.IllegalStateException: firstName must not be null
    at com.project.User.(User.kt:8)
    

    View Slide

28. @TTGonda
    collectiveidea.com
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private final String lastName;
    
    

    View Slide

29. @TTGonda
    collectiveidea.com
    @NotNull
    public final String getFirstName() {
    return this.firstName;
    }
    @Nullable
    public final String getLastName() {
    return this.lastName;
    }
    public final void setLastName(@Nullable String var1) {
    this.lastName = var1;
    }
    }
    Intrinsics.checkParameterIsNotNull(lastName, "lastName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    
    

    View Slide

30. @TTGonda
    collectiveidea.com
    data class User(
    val firstName: String,
    var lastName: String?
    )
    
    

    View Slide

31. @TTGonda
    collectiveidea.com
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private String lastName;
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    @NotNull
    public final String getFirstName() {
    return this.firstName;
    }
    @Nullable
    public final String getLastName() {
    return this.lastName;
    }
    public final void setLastName(@Nullable String var1) {
    this.lastName = var1;
    }
    @NotNull
    public final String component1() {
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    @NotNull
    public final User copy(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    return new User(firstName, lastName);
    }
    // $FF: synthetic method
    // $FF: bridge method
    @NotNull
    public static User copy$default(User var0, String var1, String var2, int var3, Object var4) {
    if((var3 & 1) != 0) {
    var1 = var0.firstName;
    }
    if((var3 & 2) != 0) {
    var2 = var0.lastName;
    }
    return var0.copy(var1, var2);
    }
    public String toString() {
    return "User(firstName=" + this.firstName + ", lastName=" + this.lastName + ")";
    }
    public int hashCode() {
    return (this.firstName != null?this.firstName.hashCode():0) * 31 + (this.lastName != null?this.lastName.hashCode():0);
    }
    public boolean equals(Object var1) {
    if(this != var1) {
    if(var1 instanceof User) {
    User var2 = (User)var1;
    if(Intrinsics.areEqual(this.firstName, var2.firstName) && Intrinsics.areEqual(this.lastName, var2.lastName)) {
    return true;
    }
    }
    return false;
    } else {
    return true;
    }
    }
    }
    
    

    View Slide

32. @TTGonda
    collectiveidea.com
    @NotNull
    public final String component1() {
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    }
    public final void setLastName(@Nullable String
    this.lastName = var1;
    }
    
    

    View Slide

33. @TTGonda
    collectiveidea.com
    @NotNull
    public final String component1() {
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    }
    public final void setLastName(@Nullable String
    this.lastName = var1;
    }
    
    // Destructuring Data Class Declarations
    val user = User("Victoria", "Gonda")
    val (firstname, lastname) = user
    

    View Slide

34. @TTGonda
    collectiveidea.com
    @NotNull
    public final String component1() {
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    }
    public final void setLastName(@Nullable String
    this.lastName = var1;
    }
    
    

    View Slide

35. @TTGonda
    collectiveidea.com
    @NotNull
    public final User copy(
    @NotNull String firstName, @Nullable String lastName) {
    Intrinsics
    .checkParameterIsNotNull(firstName, "firstName");
    return new User(firstName, lastName);
    }
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    
    

    View Slide

36. @TTGonda
    collectiveidea.com
    
    // $FF: synthetic method
    // $FF: bridge method
    @NotNull
    public static User copy$default(
    User var0, String var1, String var2, int var3, Object var4) {
    if((var3 & 1) != 0) {
    var1 = var0.firstName;
    }
    if((var3 & 2) != 0) {
    var2 = var0.lastName;
    }
    return var0.copy(var1, var2);
    }
    public final User copy(
    @NotNull String firstName, @Nullable String lastName) {
    Intrinsics
    .checkParameterIsNotNull(firstName, "firstName");
    return new User(firstName, lastName);
    }
    

    View Slide

37. @TTGonda
    collectiveidea.com
    public String toString() {
    return "User(firstName=" + this.firstName +
    ", lastName=" + this.lastName + ")";
    }
    if((var3 & 1) != 0) {
    var1 = var0.firstName;
    }
    if((var3 & 2) != 0) {
    var2 = var0.lastName;
    }
    return var0.copy(var1, var2);
    }
    
    

    View Slide

38. @TTGonda
    collectiveidea.com
    public int hashCode() {
    return (this.firstName != null?
    this.firstName.hashCode():0) * 31 +
    (this.lastName != null?
    this.lastName.hashCode():0);
    }
    public String toString() {
    return "User(firstName=" + this.firstName +
    ", lastName=" + this.lastName + ")";
    }
    
    

    View Slide

39. @TTGonda
    collectiveidea.com
    public boolean equals(Object var1) {
    if(this != var1) {
    if(var1 instanceof User) {
    User var2 = (User)var1;
    if(Intrinsics.areEqual(this.firstName, var2.firstName) &&
    Intrinsics.areEqual(this.lastName, var2.lastName)) {
    return true;
    }
    }
    return false;
    } else {
    return true;
    }
    }
    }
    this.firstName.hashCode():0) * 31 +
    (this.lastName != null?
    this.lastName.hashCode():0);
    }
    
    

    View Slide

40. @TTGonda
    collectiveidea.com
    public final class User {
    @NotNull
    private final String firstName;
    @Nullable
    private String lastName;
    public User(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    }
    @NotNull
    public final String getFirstName() {
    return this.firstName;
    }
    @Nullable
    public final String getLastName() {
    return this.lastName;
    }
    public final void setLastName(@Nullable String ) {
    this.lastName = ;
    }
    @NotNull
    public final String component1() {
    return this.firstName;
    }
    @Nullable
    public final String component2() {
    return this.lastName;
    }
    @NotNull
    public final User copy(@NotNull String firstName, @Nullable String lastName) {
    Intrinsics.checkParameterIsNotNull(firstName, "firstName");
    return new User(firstName, lastName);
    }
    // $FF: synthetic method
    // $FF: bridge method
    @NotNull
    public static User copy$default(User var0, String var1, String var2, int var3, Object var4) {
    if((var3 & 1) != 0) {
    var1 = var0.firstName;
    }
    if((var3 & 2) != 0) {
    var2 = var0.lastName;
    }
    return var0.copy(var1, var2);
    }
    public String toString() {
    return "User(firstName=" + this.firstName + ", lastName=" + this.lastName + ")";
    }
    public int hashCode() {
    return (this.firstName != null?this.firstName.hashCode():0) * 31 + (this.lastName != null?this.lastName.hashCode():0);
    }
    public boolean equals(Object var1) {
    if(this != var1) {
    if(var1 instanceof User) {
    User var2 = (User)var1;
    if(Intrinsics.areEqual(this.firstName, var2.firstName) && Intrinsics.areEqual(this.lastName, var2.lastName)) {
    return true;
    }
    }
    return false;
    } else {
    return true;
    }
    }
    }
    
    

    View Slide

41. @TTGonda
    collectiveidea.com
    data class User(
    val firstName: String = "Victoria",
    var lastName: String?
    )
    Default Values
    
    

    View Slide

42. @TTGonda
    collectiveidea.com
    val user = User(

    lastName = "Gonda"
    )
    Named Parameters
    
    

    View Slide

43. @TTGonda
    collectiveidea.com
    Null Safety
    

    View Slide

44. @TTGonda
    collectiveidea.com
    // Wont compile

    var maybeString: String? = "Hello"

    maybeString.length
    
    

    View Slide

45. @TTGonda
    collectiveidea.com
    Safe Call Operator
    val maybeString: String? = "Hello"
    maybeString?.length
    
    

    View Slide

46. @TTGonda
    collectiveidea.com
    String maybeString = "Hello";
    maybeString.length();
    
    ? ? ?
    

    View Slide

47. @TTGonda
    collectiveidea.com
    Safe Call Operator
    val maybeString: String? = null
    maybeString?.length
    
    

    View Slide

48. @TTGonda
    collectiveidea.com
    String maybeString = (String) null;
    if(maybeString != null) {
    maybeString.length();
    }
    
    

    View Slide

49. @TTGonda
    collectiveidea.com
    val maybeString: String? = null
    maybeString!!.length // NPE!
    
    

    View Slide

50. @TTGonda
    collectiveidea.com
    String maybeString = (String) null;
    if(maybeString == null) {
    Intrinsics.throwNpe();
    }
    maybeString.length();
    
    

    View Slide

51. @TTGonda
    collectiveidea.com
    val maybeString: String? = null
    maybeString?.let { string ->
    string.length
    }
    
    let
    

    View Slide

52. @TTGonda
    collectiveidea.com
    String maybeString = (String) null;
    if(maybeString != null) {
    String string = (String)maybeString;
    string.length();
    }
    
    let
    

    View Slide

53. @TTGonda
    collectiveidea.com
    val maybeString: String? = null
    

    return maybeString?.length ?: 0
    
    Elvis Operator ?:
    

    View Slide

54. @TTGonda
    collectiveidea.com
    String maybeString = (String)null;
    

    if(maybeString != null) {

    return maybeString.length();

    } else {

    return 0;
    }
    
    Elvis Operator ?:
    

    View Slide

55. @TTGonda
    collectiveidea.com
    Delegation
    

    View Slide

56. @TTGonda
    collectiveidea.com
    class CopyPrinter(copier: Copy, printer: Print)
    : Copy by copier, Print by printer
    interface Copy {
    fun copy(page: Page): Page
    }
    interface Print {
    fun print(page: Page)
    }
    
    

    View Slide

57. @TTGonda
    collectiveidea.com
    public final class CopyPrinter implements Copy, Print {
    // $FF: synthetic field
    private final Copy $$delegate_0;
    // $FF: synthetic field
    private final Print $$delegate_1;
    public CopyPrinter(@NotNull Copy copier, @NotNull Print printer) {
    Intrinsics.checkParameterIsNotNull(copier, "copier");
    Intrinsics.checkParameterIsNotNull(printer, "printer");
    super();
    this.$$delegate_0 = copier;
    this.$$delegate_1 = printer;
    }
    @NotNull
    public Page copy(@NotNull Page page) {
    Intrinsics.checkParameterIsNotNull(page, "page");
    return this.$$delegate_0.copy(page);
    }
    public void print(@NotNull Page page) {
    Intrinsics.checkParameterIsNotNull(page, "page");
    this.$$delegate_1.print(page);
    }
    }
    public interface Copy {
    @NotNull
    Page copy(@NotNull Page var1);
    }
    public interface Print {
    void print(@NotNull Page var1);
    }
    
    

    View Slide

58. @TTGonda
    collectiveidea.com
    public final class CopyPrinter
    implements Copy, Print {
    
    

    View Slide

59. @TTGonda
    collectiveidea.com
    // $FF: synthetic field
    private final Copy $$delegate_0;
    // $FF: synthetic field
    private final Print $$delegate_1;
    public final class CopyPrinter
    implements Copy, Print {
    
    

    View Slide

60. @TTGonda
    collectiveidea.com
    public CopyPrinter(
    @NotNull Copy copier,
    @NotNull Print printer) {
    Intrinsics
    .checkParameterIsNotNull(copier, "copier");
    Intrinsics
    .checkParameterIsNotNull(printer, "printer");
    super();
    this.$$delegate_0 = copier;
    this.$$delegate_1 = printer;
    }
    // $FF: synthetic field
    private final Copy $$delegate_0;
    // $FF: synthetic field
    private final Print $$delegate_1;
    
    

    View Slide

61. @TTGonda
    collectiveidea.com
    @NotNull
    public Page copy(@NotNull Page page) {
    Intrinsics
    .checkParameterIsNotNull(page, "page");
    return this.$$delegate_0.copy(page);
    }
    public void print(@NotNull Page page) {
    Intrinsics
    .checkParameterIsNotNull(page, "page");
    this.$$delegate_1.print(page);
    }
    }
    super();
    this.$$delegate_0 = copier;
    this.$$delegate_1 = printer;
    }
    
    

    View Slide

62. @TTGonda
    collectiveidea.com
    public interface Copy {
    @NotNull
    Page copy(@NotNull Page var1);
    }
    public interface Print {
    void print(@NotNull Page var1);
    }
    public void print(@NotNull Page page) {
    Intrinsics
    .checkParameterIsNotNull(page, "page");
    this.$$delegate_1.print(page);
    }
    }
    
    

    View Slide

63. @TTGonda
    collectiveidea.com
    public final class CopyPrinter implements Copy, Print {
    // $FF: synthetic field
    private final Copy $$delegate_0;
    // $FF: synthetic field
    private final Print $$delegate_1;
    public CopyPrinter(@NotNull Copy copier, @NotNull Print printer) {
    Intrinsics.checkParameterIsNotNull(copier, "copier");
    Intrinsics.checkParameterIsNotNull(printer, "printer");
    super();
    this.$$delegate_0 = copier;
    this.$$delegate_1 = printer;
    }
    @NotNull
    public Page copy(@NotNull Page page) {
    Intrinsics.checkParameterIsNotNull(page, "page");
    return this.$$delegate_0.copy(page);
    }
    public void print(@NotNull Page page) {
    Intrinsics.checkParameterIsNotNull(page, "page");
    this.$$delegate_1.print(page);
    }
    }
    public interface Copy {
    @NotNull
    Page copy(@NotNull Page var1);
    }
    public interface Print {
    void print(@NotNull Page var1);
    }
    
    

    View Slide

64. @TTGonda
    collectiveidea.com
    Class Extensions
    

    View Slide

65. @TTGonda
    collectiveidea.com
    Class Extensions
    TextUtils.isEmpty("hello");
    

    View Slide

66. @TTGonda
    collectiveidea.com
    // StringExt.kt
    fun String.double(): String {
    return this + this
    }
    
    

    View Slide

67. @TTGonda
    collectiveidea.com
    "hello".double()
    // -> “hellohello”
    // StringExt.kt
    fun String.double(): String {
    return this + this
    }
    
    

    View Slide

68. @TTGonda
    collectiveidea.com
    public final class StringExtKt {
    @NotNull
    public static final String double(
    @NotNull String $receiver) {
    Intrinsics
    .checkParameterIsNotNull($receiver, "$receiver");
    return $receiver + $receiver;
    }
    }
    
    

    View Slide

69. @TTGonda
    collectiveidea.com
    StringExtKt.double("hello");
    // -> "hellohello"
    public final class StringExtKt {
    @NotNull
    public static final String double(
    @NotNull String $receiver) {
    Intrinsics
    .checkParameterIsNotNull($receiver, "$r
    return $receiver + $receiver;
    }
    }
    
    

    View Slide

70. @TTGonda
    collectiveidea.com
    Lambdas
    

    View Slide

71. @TTGonda
    collectiveidea.com
    fun firstNSquares(n: Int): Array
    = Array(n, { i -> i * i })
    // firstNSquares(3)
    // -> [0, 1, 4]
    
    

    View Slide

72. @TTGonda
    collectiveidea.com
    @NotNull
    public static final Integer[] firstNSquares(int n) {
    Integer[] result$iv = new Integer[n];
    int i$iv = 0;
    int var3 = n - 1;
    if(i$iv <= var3) {
    while(true) {
    Integer var9 = Integer.valueOf(i$iv * i$iv);
    result$iv[i$iv] = var9;
    if(i$iv == var3) {
    break;
    }
    ++i$iv;
    }
    }
    return (Integer[])((Object[])result$iv);
    }
    
    

    View Slide

73. @TTGonda
    collectiveidea.com
    @NotNull
    public static Integer[] firstNSquares(int n) {
    Integer[] resultArray = new Integer[n];
    int i = 0;
    int max = n - 1;
    if(i <= max) {
    while(true) {
    Integer square = i * i;
    resultArray[i] = square;
    if(i == max) {
    break;
    }
    ++i;
    }
    }
    return resultArray;
    }
    
    

    View Slide

74. @TTGonda
    collectiveidea.com
    fun firstNSquares(n: Int): Array
    = Array(n, { i -> square(i + 1) })
    // firstNSquares(3)
    // -> [1, 4, 9]
    
    

    View Slide

75. @TTGonda
    collectiveidea.com
    @NotNull
    public static Integer[] firstNSquares(int n) {
    Integer[] resultArray = new Integer[n];
    int i = 0;
    int max = n - 1;
    if(i <= max) {
    while(true) {
    Integer square = square(i+1);
    resultArray[i] = square;
    if(i == max) {
    break;
    }
    ++i;
    }
    }
    return resultArray;
    }
    
    

    View Slide

76. @TTGonda
    collectiveidea.com
    inline fun beforeAndAfter(
    startString: String,
    function: (string: String) -> String) {
    print("Before: $startString")
    val after = function(startString)
    print("After: $after")
    }
    
    

    View Slide

77. @TTGonda
    collectiveidea.com
    inline fun beforeAndAfter(
    startString: String,
    function: (string: String) -> String) {
    print("Before: $startString")
    val after = function(startString)
    print("After: $after")
    }
    
    public inline fun T.let(block: (T) -> R): R
    = block(this)
    

    View Slide

78. @TTGonda
    collectiveidea.com
    inline fun beforeAndAfter(
    startString: String,
    function: (string: String) -> String) {
    print("Before: $startString")
    val after = function(startString)
    print("After: $after")
    }
    
    

    View Slide

79. @TTGonda
    collectiveidea.com
    public final void beforeAndAfter(
    @NotNull String startString,
    @NotNull Function1 function) {
    Intrinsics
    .checkParameterIsNotNull(startString, "startString");
    Intrinsics
    .checkParameterIsNotNull(function, "function");
    String after = "Before: " + startString;
    System.out.print(after);
    after = (String)function.invoke(startString);
    String var4 = "After: " + after;
    System.out.print(var4);
    }
    

    View Slide

80. @TTGonda
    collectiveidea.com
    public final void beforeAndAfter(
    @NotNull String startString,
    @NotNull Function1 function) {
    Intrinsics
    .checkParameterIsNotNull(startString, "startString");
    Intrinsics
    .checkParameterIsNotNull(function, "function");
    String after = "Before: " + startString;
    System.out.print(after);
    after = (String)function.invoke(startString);
    String var4 = "After: " + after;
    System.out.print(var4);
    }
    public interface Function1 : Function {
    public operator fun invoke(p1: P1): R
    }
    

    View Slide

81. @TTGonda
    collectiveidea.com
    public final void beforeAndAfter(
    @NotNull String startString,
    @NotNull Function1 function) {
    Intrinsics
    .checkParameterIsNotNull(startString, "startString");
    Intrinsics
    .checkParameterIsNotNull(function, "function");
    String after = "Before: " + startString;
    System.out.print(after);
    after = (String)function.invoke(startString);
    String var4 = "After: " + after;
    System.out.print(var4);
    }
    

    View Slide

82. @TTGonda
    collectiveidea.com
    fun example() {
    beforeAndAfter("hello", { string -> string + " world" })
    }
    // Output
    “Before: hello"
    “After: hello world"
    
    

    View Slide

83. @TTGonda
    collectiveidea.com
    public final void example() {
    String startString$iv = "hello";
    String after$iv = "Before: " + startString$iv;
    System.out.print(after$iv);
    String string = (String)startString$iv;
    after$iv = (String)(string + " world");
    string = "After: " + after$iv;
    System.out.print(string);
    }
    
    

    View Slide

84. @TTGonda
    collectiveidea.com
    beforeAndAfter("hello", { string -> string + " world" })
    

    beforeAndAfter("hello", { it + " world" })
    

    beforeAndAfter("hello") { it + " world" }
    
    Lambda Parameters
    

    View Slide

85. @TTGonda
    collectiveidea.com
    fun beforeAndAfter(
    startString: String,
    function: (string: String) -> String
    ) {
    print("Before: $startString")
    val after = function(startString)
    print("After: $after")
    }
    
    

    View Slide

86. @TTGonda
    collectiveidea.com
    public final void example() {
    this.beforeAndAfter("hello", (Function1)null.INSTANCE);
    }
    // Output
    “Before: hello”
    “After: hello world”
    
    

    View Slide

87. @TTGonda
    collectiveidea.com
    

    View Slide

88. @TTGonda
    collectiveidea.com
    // Pseudocode for bytecode
    final class BytecodeClass
    extends Lambda
    implements Function1 {
    public void invoke(String string) {
    StringBuilder sb = new StringBuilder("hello");
    sb.append(" world");
    returnValue = sb.toString();
    }
    static Function1 INSTANCE = new BytecodeClass();
    }
    

    View Slide

89. @TTGonda
    collectiveidea.com
    // Pseudocode for bytecode
    final class BytecodeClass
    extends Lambda
    implements Function1 {
    public void invoke(String string) {
    StringBuilder sb = new StringBuilder("hello");
    sb.append(" world");
    returnValue = sb.toString();
    }
    static Function1 INSTANCE = new BytecodeClass();
    }
    public final void example() {
    this.beforeAndAfter("hello", (Function1)null.INSTANCE);
    }
    

    View Slide

90. @TTGonda
    collectiveidea.com
    // Pseudocode for bytecode
    final class BytecodeClass
    extends Lambda
    implements Function1 {
    public void invoke(String string) {
    StringBuilder sb = new StringBuilder("hello");
    sb.append(" world");
    returnValue = sb.toString();
    }
    static Function1 INSTANCE = new BytecodeClass();
    }
    

    View Slide

91. @TTGonda
    collectiveidea.com
    Companion Objects
    Smart Casting
    Collection Functions
    Control Flow Structures
    Operator Overloading
    Named Parameters
    

    View Slide

92. @TTGonda
    collectiveidea.com
    Menu > Tools > Kotlin > Show Kotlin Bytecode
    or
    CMD+SHFT+A and search “Show Kotlin Bytecode”
    

    View Slide

93. @TTGonda
    collectiveidea.com
    Code > Convert Java File to Kotlin File
    or
    CMD+SHFT+A and search “Convert Java File to Kotlin File”
    

    View Slide

94. @TTGonda
    collectiveidea.com
    DETOUR
    JAVA
    

    View Slide

95. @TTGonda
    collectiveidea.com
    Thanks!
    Victoria Gonda
    www.victoriagonda.com
    @TTGonda
    

    View Slide