Dekompiling (droidcon Berlin 2019)

Kotlin has many features that are leaps and bounds ahead of Java. However, its primary target platform being the JVM, all of these features still need to compile to the same bytecode as Java does. This is a look at how a variety of interesting Kotlin features are compiled to bytecode, and what their Java equivalents would be. Even though Kotlin abstracts away much of the virtual machine and the original feature set of Java with its own features, it’s still important to know what your Kotlin code compiles to. Not only can this knowledge give you the power to optimize your code, but it will also help you avoid subtle bugs that would otherwise be near impossible to track down.

Talk recording (re-recorded after the conference): https://www.droidcon.com/media-detail?video=370862982

Transcript

1. Dekompiling
   Márton Braun zsmb.co zsmb13
   braun.marton@autsoft.hu
   

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2. hello
   

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3. multiply("hello ", 3)
   

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4. fun main() {
   println( )
   }
   multiply("hello ", 3)
   

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5. "hello hello hello "
   fun main() {
   println(multiply("hello ", 3))
   }
   

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6. fun main() {
   println(multiply("hello ", 3))
   }
   

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7. fun main() {
   println(multiply("hello ", 3))
   }
   

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8. fun main() {
   println(multiply("hello ", 3))
   }
   

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9. fun main() {
   println(multiply("hello ", 3))
   }
   

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10. fun main() {
    println(multiply("hello ", 3))
    }
    

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11. fun main() {
    println(multiply("hello ", 3))
    }
    

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12. fun main() {
    println(multiply("hello ", 3))
    }
    

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13. fun main() {
    println(multiply("hello ", 3))
    }
    

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14. // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    

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15. // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    

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16. // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    

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17. // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    

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18. fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    

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19. fun main() {
    println(multiply("hello ", 3))
    }
    public final class DecKt {
    public static final void main() {
    String var0 = multiply("hello ", 3);
    boolean var1 = false;
    System.out.println(var0);
    }
    }
    // access flags 0x19
    public final static main()V
    L0
    LINENUMBER 2 L0
    LDC "hello "
    ICONST_3
    INVOKESTATIC DecKt.multiply
    (Ljava/lang/String;I)Ljava/lang/String;
    ASTORE 0
    L1
    ICONST_0
    ISTORE 1
    L2
    GETSTATIC java/lang/System.out :
    Ljava/io/PrintStream;
    ALOAD 0
    INVOKEVIRTUAL java/io/PrintStream.println
    (Ljava/lang/Object;)V
    L3
    L4
    LINENUMBER 3 L4
    RETURN
    L5
    MAXSTACK = 2
    MAXLOCALS = 2
    .java
    .kt
    .class
    

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20. fun main() {
    println(multiply("hello ", 3))
    }
    "hello hello hello "
    

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21. fun main() {
    println( )
    }
    multiply("hello ", 3) "hello hello hello "
    fun multiply(string: String, times: Int): String {
    }
    

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22. fun main() {
    println( )
    }
    multiply("hello ", 3) "hello hello hello "
    fun multiply(string: String, times: Int): String {
    var result = ""
    }
    

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23. fun main() {
    println( )
    }
    multiply("hello ", 3) "hello hello hello "
    fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    }
    }
    

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24. fun main() {
    println( )
    }
    multiply("hello ", 3) "hello hello hello "
    fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    }
    

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25. fun main() {
    println( )
    }
    multiply("hello ", 3) "hello hello hello "
    fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    

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26. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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27. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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28. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    Int?
    @Nullable Integer
    

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29. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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30. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    public class Intrinsics {
    public static void checkParameterIsNotNull(
    Object value, String paramName
    ) {
    if (value == null) {
    throwParameterIsNullException(paramName);
    }
    }
    private static void throwParameterIsNullException(
    String paramName
    ) {
    // ...
    throw new IllegalArgumentException(
    "Parameter specified as non-null is null: " +
    "method " + className + "." + methodName +
    ", parameter " + paramName);
    }
    }
    

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31. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    public class Intrinsics {
    public static void checkParameterIsNotNull(
    Object value, String paramName
    ) {
    if (value == null) {
    throwParameterIsNullException(paramName);
    }
    }
    private static void throwParameterIsNullException(
    String paramName
    ) {
    // ...
    throw new IllegalArgumentException(
    "Parameter specified as non-null is null: " +
    "method " + className + "." + methodName +
    ", parameter " + paramName);
    }
    }
    

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32. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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33. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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34. fun multiply(string: String, times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + string
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    

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35. fun string: String,
    var result = ""
    for (i in 0 until times) {
    result = result +
    }
    return result
    }
    @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    times: Int): String {
    string
    multiply(
    

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36. @NotNull
    public static final String multiply(@NotNull String string, int times) {
    Intrinsics.checkParameterIsNotNull(string, "string");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + string;
    }
    return result;
    }
    fun String.
    var result = ""
    for (i in 0 until times) {
    result = result +
    }
    return result
    }
    times: Int): String {
    this
    multiply(
    

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37. fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    );
    @NotNull
    public static final String multiply(@NotNull String
    Intrinsics.checkParameterIsNotNull(
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result +
    }
    return result;
    }
    , int times) {
    string
    "string"
    ,
    string
    string;
    

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38. @NotNull
    public static final String multiply(@NotNull String $this$multiply, int time
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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39. @NotNull
    public static final String multiply(@NotNull String $this$multiply, int time
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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40. @NotNull
    public static final String multiply(@NotNull String $this$multiply, int time
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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41. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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42. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    {
    open
    }
    {
    override
    }
    class Cat : Animal()
    fun main() {
    val animal: Animal = Cat()
    animal.identify()
    }
    println("This is a cat!")
    }
    identify() {
    fun
    abstract class Animal
    identify() {
    fun
    println("This is an animal.")
    }
    

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43. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    {
    open
    }
    {
    override
    }
    class Cat : Animal()
    fun main() {
    val animal: Animal = Cat()
    animal.identify()
    }
    println("This is a cat!")
    }
    identify() {
    fun
    abstract class Animal
    identify() {
    fun
    println("This is an animal.")
    }
    "This is a cat!"
    

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44. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    class Cat : Animal()
    fun main() {
    val animal: Animal = Cat()
    animal.identify()
    }
    println("This is a cat!")
    }
    identify() {
    fun
    abstract class Animal
    identify() {
    println("This is an animal.")
    }
    fun Animal.
    Cat.
    

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45. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    class Cat : Animal()
    fun main() {
    val animal: Animal = Cat()
    animal.identify()
    }
    println("This is a cat!")
    }
    identify() {
    Animal.
    Cat.
    fun
    abstract class Animal
    identify() {
    println("This is an animal.")
    }
    fun
    "This is an animal."
    

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46. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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47. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result = result + this
    }
    return result
    }
    

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48. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

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49. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

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50. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

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51. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    a += b a.plusAssign(b)
    a -= b a.minusAssign(b)
    

    View Slide

52. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    a = a + b
    a = a - b
    a += b a.plusAssign(b)
    a -= b a.minusAssign(b)
    

    View Slide

53. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    a = a + b
    a = a - b
    a += b a.plusAssign(b)
    a -= b a.minusAssign(b)
    a + b a.plus(b)
    a - b a.minus(b)
    

    View Slide

54. @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    result = result + $this$multiply;
    }
    return result;
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

    View Slide

55. fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

    View Slide

56. fun repeat(times: Int, action: () -> Unit) {
    action()
    }
    for (i in 0 until times) {
    }
    fun String.multiply(times: Int): String {
    var result = ""
    for (i in 0 until times) {
    result += this
    }
    return result
    }
    

    View Slide

57. fun String.multiply(times: Int): String {
    var result = ""
    repeat(times) {
    result += this
    }
    return result
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

58. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

59. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

60. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    package kotlin.jvm.functions
    /** A function that takes 0 arguments. */
    public interface Function0 : Function {
    /** Invokes the function. */
    public operator fun invoke(): R
    }
    

    View Slide

61. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    package kotlin.jvm.functions
    /** A function that takes 0 arguments. */
    public interface Function0 : Function {
    /** Invokes the function. */
    public operator fun invoke(): R
    }
    /** A function that takes 1 argument. */
    public interface Function1 : Function {
    /** Invokes the function with the specified argument. */
    public operator fun invoke(p1: P1): R
    }
    

    View Slide

62. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

63. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

64. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

65. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

    View Slide

66. fun String.multiply(times: Int): String {
    var result = ""
    repeat(times) {
    result += this
    }
    return result
    }
    public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var2 = 0;
    for (int var3 = times; var2 < var3; ++var2) {
    action.invoke();
    }
    }
    

    View Slide

67. });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

68. });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

69. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

70. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    String result = "";
    return result;
    

    View Slide

71. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    String result = "";
    return result;
    result += $this$multiply;
    

    View Slide

72. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    String result = "";
    return result;
    result += $this$multiply;
    

    View Slide

73. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    final String result = "";
    return result;
    result += $this$multiply;
    

    View Slide

74. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    final String result = "";
    return result;
    result += $this$multiply;
    

    View Slide

75. });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    final String result = "";
    return result;
    result += $this$multiply;
    ""
    result
    String
    

    View Slide

76. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    final String result = "";
    return result;
    result += $this$multiply;
    "hi"
    result
    String
    

    View Slide

77. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    final String result = "";
    return result;
    result += $this$multiply;
    "hi"
    result
    String
    ""
    result
    String
    

    View Slide

78. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

79. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final class ObjectRef {
    public T element;
    @Override
    public String toString() {
    return String.valueOf(element);
    }
    }
    

    View Slide

80. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

81. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    ""
    result
    String
    ""
    result
    String
    

    View Slide

82. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    ""
    result
    String
    ""
    result
    String
    ""
    result
    String
    element
    ObjectRef
    

    View Slide

83. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    ""
    result
    String
    ""
    result
    String
    "hi"
    ObjectRef
    result
    String
    element
    

    View Slide

84. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

85. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    fun example() {
    repeat(20) {
    println("Ni.")
    }
    }
    

    View Slide

86. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    fun example() {
    repeat(20) {
    println("Ni.")
    }
    }
    public static final void example() {
    repeat(20, (Function0) null.INSTANCE);
    }
    

    View Slide

87. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    fun example() {
    repeat(20) {
    println("Ni.")
    }
    }
    public static final void example() {
    repeat(20, (Function0) null.INSTANCE);
    }
    

    View Slide

88. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final void example() {
    repeat(20, (Function0) null.INSTANCE);
    }
    final class NiKt$example$1 implements Function0 {
    public static final NiKt$example$1 INSTANCE =
    new NiKt$example$1();
    public final void invoke() {
    String str = "Ni.";
    System.out.println(str);
    }
    }
    

    View Slide

89. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final void example() {
    repeat(20, (Function0) null.INSTANCE);
    }
    final class NiKt$example$1 implements Function0 {
    public static final NiKt$example$1 INSTANCE =
    new NiKt$example$1();
    public final void invoke() {
    String str = "Ni.";
    System.out.println(str);
    }
    }
    

    View Slide

90. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final void example() {
    repeat(20, (Function0) null.INSTANCE);
    }
    final class NiKt$example$1 implements Function0 {
    public static final NiKt$example$1 INSTANCE =
    new NiKt$example$1();
    public final void invoke() {
    String str = "Ni.";
    System.out.println(str);
    }
    }
    

    View Slide

91. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final void example() {
    repeat(20, (Function0) NiKt$example$1.INSTANCE);
    }
    final class NiKt$example$1 implements Function0 {
    public static final NiKt$example$1 INSTANCE =
    new NiKt$example$1();
    public final void invoke() {
    String str = "Ni.";
    System.out.println(str);
    }
    }
    

    View Slide

92. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    public static final void example() {
    repeat(20, (Function0) NiKt$example$1.INSTANCE);
    }
    final class NiKt$example$1 implements Function0 {
    public static final NiKt$example$1 INSTANCE =
    new NiKt$example$1();
    public final void invoke() {
    String str = "Ni.";
    System.out.println(str);
    }
    }
    

    View Slide

93. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

    View Slide

94. // ...
    });
    return (String) result.element;
    }
    @NotNull public static final
    String multiply(@NotNull final String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    final ObjectRef result = new ObjectRef();
    result.element = "";
    repeat(times, new Function0() {
    public final void invoke() {
    ObjectRef var10000 = result;
    String var10001 = (String) var10000.element;
    var10000.element = var10001 + $this$multiply;
    }
    

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95. fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

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96. inline fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

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97. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    action.invoke();
    }
    }
    inline fun repeat(times: Int, action: () -> Unit) {
    for (i in 0 until times) {
    action()
    }
    }
    

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98. public static final void repeat(int times, @NotNull Function0 action) {
    Intrinsics.checkParameterIsNotNull(action, "action");
    int var3 = 0;
    for (int var4 = times; var3 < var4; ++var3) {
    action.invoke();
    }
    }
    fun String.multiply(times: Int): String {
    var result = ""
    repeat(times) {
    result += this
    }
    return result
    }
    

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99. fun String.multiply(times: Int): String {
    var result = ""
    repeat(times) {
    result += this
    }
    return result
    }
    @NotNull public static final
    String multiply(@NotNull String $this$multiply, int times) {
    Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
    String result = "";
    int var4 = 0;
    for (int var5 = times; var4 < var5; ++var4) {
    result = result + $this$multiply;
    }
    return result;
    }
    

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100. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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101. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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102. inline fun repeat( , action: () -> Unit) {
     for (i in 0 until ) {
     action()
     }
     }
     fun String.multiply(times: Int): String {
     var result = ""
     repeat( ) {
     result += this
     }
     return result
     }
     times
     times
     times: Int
     

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103. inline fun repeat( , action: () -> Unit) {
     for (i in 0 until ) {
     action()
     }
     }
     times
     fun String.multiply(times: Int): String {
     var result = ""
     repeat( ) {
     result += this
     }
     return result
     }
     

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104. inline fun repeat( , ) {
     for (i in 0 until ) {
     }
     }
     times
     fun String.multiply(times: Int): String {
     var result = ""
     repeat( )
     return result
     }
     action
     action: () -> Unit
     }
     {
     result += this
     ()
     

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105. inline fun repeat( , ) {
     for (i in 0 until ) {
     }
     }
     ()
     fun String.multiply(times: Int): String {
     var result = ""
     repeat( )
     return result
     }
     { result += this }
     times
     

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106. inline fun repeat( , ) {
     }
     for (i in 0 until times) {
     result += this
     }
     fun String.multiply(times: Int): String {
     var result = ""
     return result
     }
     repeat( )
     

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107. for (i in 0 until times) {
     result += this
     }
     fun String.multiply(times: Int): String {
     var result = ""
     return result
     }
     repeat( )
     

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108. fun String.multiply(times: Int): String {
     var result = ""
     return result
     }
     for (i in 0 until times) {
     result += this
     }
     

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109. fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     

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110. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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111. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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112. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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113. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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114. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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115. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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116. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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117. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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118. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     ALOAD 2
     NEW java/lang/StringBuilder
     DUP
     INVOKESPECIAL java/lang/StringBuilder. ()V
     SWAP
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     ALOAD 0
     INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
     Ljava/lang/StringBuilder;
     INVOKEVIRTUAL java/lang/StringBuilder.toString ()
     Ljava/lang/String;
     fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     

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119. fun String.multiply(times: Int): String {
     var result = ""
     repeat(times) {
     result += this
     }
     return result
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     

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120. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     

     View Slide

121. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     @NotNull public static final
     String multiply(@NotNull String $this$multiply, int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     StringBuilder builder = new StringBuilder();
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     builder.append($this$multiply);
     }
     String var100 = builder.toString();
     Intrinsics.checkExpressionValueIsNotNull(var100, "builder.toString()");
     return var100;
     }
     

     View Slide

122. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     @NotNull public static final
     String multiply(@NotNull String $this$multiply, int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     StringBuilder builder = new StringBuilder();
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     builder.append($this$multiply);
     }
     String var100 = builder.toString();
     Intrinsics.checkExpressionValueIsNotNull(var100, "builder.toString()");
     return var100;
     }
     

     View Slide

123. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     @NotNull public static final
     String multiply(@NotNull String $this$multiply, int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     StringBuilder builder = new StringBuilder();
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     builder.append($this$multiply);
     }
     String var100 = builder.toString();
     Intrinsics.checkExpressionValueIsNotNull(var100, "builder.toString()");
     return var100;
     }
     

     View Slide

124. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     

     View Slide

125. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

     View Slide

126. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

     View Slide

127. fun String.multiply(times: Int): String {
     val builder = StringBuilder()
     repeat(times) {
     builder.append(this)
     }
     return builder.toString()
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

     View Slide

128. fun String.multiply(times: Int): String {
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     repeat(times) {
     append(this)
     }
     }
     return buildString {
     

     View Slide

129. fun String.multiply(times: Int): String {
     return buildString {
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     repeat(times) {
     append(this)
     }
     

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130. fun String.multiply(times: Int): String {
     return buildString {
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     repeat(times) {
     this.append(this)
     }
     

     View Slide

131. fun String.multiply(times: Int): String {
     return buildString {
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     repeat(times) {
     this.append(this)
     }
     

     View Slide

132. fun String.multiply(times: Int): String {
     return buildString {
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     repeat(times) {
     this.append(this)
     }
     

     View Slide

133. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     }
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     append(this@multiply)
     this.
     

     View Slide

134. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     }
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     append(this@multiply)
     this.
     

     View Slide

135. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     append(this@multiply)
     this.
     

     View Slide

136. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     });
     }
     

     View Slide

137. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     });
     }
     

     View Slide

138. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     });
     }
     

     View Slide

139. inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     });
     }
     

     View Slide

140. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     }
     });
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     }
     

     View Slide

141. return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     }
     });
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

     View Slide

142. return buildString(new Function1() {
     public void invoke(@NotNull StringBuilder $this$buildString) {
     Intrinsics.checkParameterIsNotNull($this$buildString, "...");
     }
     });
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

     View Slide

143. inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     StringBuilder $this$buildString = new StringBuilder();
     String var10000 = $this$buildString.toString();
     Intrinsics.checkExpressionValueIsNotNull(var10000, "...");
     return var10000;
     @NotNull public static final
     String multiply(@NotNull final String $this$multiply, final int times) {
     Intrinsics.checkParameterIsNotNull($this$multiply, "$this$multiply");
     int var4 = 0;
     for (int var5 = times; var4 < var5; ++var4) {
     $this$buildString.append($this$multiply);
     }
     }
     

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144. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

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145. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     

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146. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     package kotlin.text
     @kotlin.internal.InlineOnly
     public inline fun buildString(
     builderAction: StringBuilder.() -> Unit
     ): String = StringBuilder().apply(builderAction).toString()
     package kotlin
     @kotlin.internal.InlineOnly
     public inline fun repeat(times: Int, action: (Int) -> Unit) {
     contract { callsInPlace(action) }
     for (index in 0 until times) {
     action(index)
     }
     }
     

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147. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     package kotlin.text
     @kotlin.internal.InlineOnly
     public inline fun buildString(
     builderAction: StringBuilder.() -> Unit
     ): String = StringBuilder().apply(builderAction).toString()
     package kotlin
     @kotlin.internal.InlineOnly
     public inline fun repeat(times: Int, action: (Int) -> Unit) {
     contract { callsInPlace(action) }
     for (index in 0 until times) {
     action(index)
     }
     }
     

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148. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     inline fun repeat(times: Int, action: () -> Unit) {
     for (i in 0 until times) {
     action()
     }
     }
     inline fun buildString(builderAction: StringBuilder.() -> Unit): String {
     val builder = StringBuilder()
     builder.builderAction()
     return builder.toString()
     }
     package kotlin.text
     @kotlin.internal.InlineOnly
     public inline fun buildString(
     builderAction: StringBuilder.() -> Unit
     ): String = StringBuilder().apply(builderAction).toString()
     package kotlin
     @kotlin.internal.InlineOnly
     public inline fun repeat(times: Int, action: (Int) -> Unit) {
     contract { callsInPlace(action) }
     for (index in 0 until times) {
     action(index)
     }
     }
     

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149. fun String.multiply(times: Int): String {
     return buildString {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     

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150. fun String.multiply(times: Int): String {
     return buildString(capacity = length * times) {
     repeat(times) {
     append(this@multiply)
     }
     }
     }
     

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151. Related talks
     • Kotlin: Uncovered
      Victoria Gonda, Chicago Roboto 2017
      https://vimeo.com/217569130
     • Desugaring Kotlin features and their performance impact
      Ionuț Baloșin, VoxxedDays Bucharest 2019
      https://www.youtube.com/watch?v=D2a2vK-mfp4
     • Kotlin Under the Hood
      Chet Haase & Romain Guy, I/O ’19
      https://www.youtube.com/watch?v=Ta5wBJsC39s
     

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152. References
     • Execution in the Kingdom of Nouns
      https://steve-yegge.blogspot.com/2006/03/execution-in-
     kingdom-of-nouns.html
     • Kotlin 1.3 changes to functional types
      https://kotlinlang.org/docs/reference/whatsnew13.html#functio
     ns-with-big-arity
     

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153. zsmb13
     zsmb.co/talks
     

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154. Questions?
     Márton Braun zsmb.co zsmb13
     braun.marton@autsoft.hu
     

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