Hey Kotlin, how it works?

Let's dive into Kotlin features and how it works.
I'm keeping updating the slides whenever I got new things. :)

You can find articles on this topic at:
- https://goo.gl/2Tyx4B (eng.)
- https://goo.gl/H9iih9 (kor.)

Transcript

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3. https://goo.gl/2Tyx4B (eng.) https://goo.gl/H9iih9 (kor.) https://goo.gl/8VdiCz (GitHub)
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11. #BTJD
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12. package com.cwdoh.devfest2017 class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null fun description() = "$speaker's talk: '$title' at room $room" }
13. WBS
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14. package com.cwdoh.devfest2017 class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null fun description() = "$speaker's talk: '$title' at room $room" }
15. class Session { var name = "cwdoh" } 1SPQFSUZ
    WBS public final class Session { @NotNull private String name = "cwdoh"; @NotNull public final String getName() { return this.name; } public final void setName(@NotNull String var1) { Intrinsics.checkParameterIsNotNull(var1, "<set-?>"); this.name = var1; } }
16. class Session { val name = "cwdoh" } 1SPQFSUZ
    WBM public final class Session { @NotNull private final String name = "cwdoh"; @NotNull public final String getName() { return this.name; } }
17. class Session { val speaker = "cwdoh" fun description() { val talks = "$speaker's talks" println(talks) } } -PDBM
    7BSJBCMF public final class Session { @NotNull private final String speaker = "cwdoh"; @NotNull public final String getSpeaker() { return this.speaker; } public final void description() { String talks = "" + this.speaker + "'s talks"; System.out.println(talks); } }
18. /VMMBCMF
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19. package com.cwdoh.devfest2017 class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null fun description() = "$speaker's talk: '$title' at room $room" }
20. class Session { var name: String = "cwdoh" } /PU/VMM
    QSPQFSUZ public final class Session { @NotNull private String name = "cwdoh"; @NotNull public final String getName() { return this.name; } public final void setName(@NotNull String var1) { Intrinsics.checkParameterIsNotNull(var1, "<set-?>"); this.name = var1; } } public static void checkParameterIsNotNull(Object value, String paramName) { if (value == null) { throwParameterIsNullException(paramName); } }
21. class Session { fun hello(name: String) = "hello, " + name } /PU/VMM
    QBSBNFUFS public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; } } public static void checkParameterIsNotNull(Object value, String paramName) { if (value == null) { throwParameterIsNullException(paramName); } }
22. class Session { fun hello(name: String) = "hello, " + name fun print() { val name: String = "cwdoh" print(hello(name)) } } /PU/VMM
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    public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; } public final void print() { String name = "cwdoh"; String var2 = this.hello(name); System.out.print(var2); } }
23. class Session { fun hello(name: String) = "hello, " + name fun print() { val name: String? = null print(hello(name!!)) } } .JYFE
    &YDFQUJPO public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; } public final void print() { String name = (String)null; Intrinsics.throwNpe(); String var2 = this.hello(name); System.out.print(var2); } } NullPointerException?
24. 4USJOH
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25. package com.cwdoh.devfest2017 class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null fun description() = "$speaker's talk: '$title' at room $room" }
26. class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null fun description() = "$speaker's talk: '$title' at room $room" } 4USJOH
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    DPODBUFOBUJPO public final class Session { @NotNull private final String speaker = "cwdoh"; @NotNull private final String title = "Kotlin: How it works"; @Nullable private Integer room; … @NotNull public final String description() { return "" + this.speaker + "'s talk: ‘" + this.title + "' at room " + this.room; } }
27. #ZUFDPEF
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    4USJOH#VJMEFS // access flags 0x11 public final description()Ljava/lang/String; @Lorg/jetbrains/annotations/NotNull;() // invisible L0 LINENUMBER 8 L0 NEW java/lang/StringBuilder DUP INVOKESPECIAL java/lang/StringBuilder.<init> ()V LDC "" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.speaker : Ljava/lang/String; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "'s talk: '" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.title : Ljava/lang/String; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "' at room " INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.room : Ljava/lang/Integer; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/Object;)Ljava/lang/StringBuilder; INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String; ARETURN
28. *OIFSJUBODF
29. class NotOpenedClass open class OpenedClass ,FZXPSE
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30. interface Interface open class OpenClass class ChildClass: OpenClass(), Interface fun test() { val child = ChildClass() } 0QFOFE
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32. class Person1 constructor(name: String) class Person2(name: String) $POTUSVDUPS public final class Person1 { public Person1(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); } } public final class Person2 { public Person2(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); } }
33. class Person constructor(val name: String) $POTUSVDUPS
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34. class Person constructor(val name: String) { val greetings: String init { greetings = "hello, $name” } } *OJUJBM[JFS public final class Person { @NotNull private String greetings; @NotNull private final String name; @NotNull public final String getGreetings() { return this.greetings; } @NotNull public final String getName() { return this.name; } public Person(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); this.name = name; this.greetings = "hello, " + this.name; } }
35. class Person constructor(val name: String) { val greetings: String var age: Int = null constructor(name: String, age: Int): this(name) { this.age = age } init { greetings = "hello, $name” } } $POTUSVDUPS
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36. 1SJPSJUJFT
37. open class Parent { private val a = println("Parent.a") constructor(arg: Unit=println("Parent primary constructor arg")) { println("Parent primary constructor") } init { println("Parent.init") } private val b = println("Parent.b") } class Child : Parent { val a = println("Child.a") init { println("Child.init 1") } constructor(arg: Unit=println("Child primary constructor arg")) : super() { println("Child primary constructor") } val b = println("Child.b") constructor(arg: Int, arg2:Unit= println("Child secondary constructor arg")): this() { println("Child secondary constructor") } init { println("Child.init 2") } } fun main(args: Array<String>) { Child(1) } Child secondary constructor arg Child primary constructor arg Parent primary constructor arg Parent.a Parent.init Parent.b Parent primary constructor Child.a Child.init 1 Child.b Child.init 2 Child primary constructor Child secondary constructor 4PVSDF
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40. class Props { var size: Int = 0 val isEmpty: Boolean get() = this.size == 0 } $VTUPN
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41. class Props { var age: Int = 0 set(value: Int) { age = if (value < 0) 0 else value } } $BVUJPO
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42. class Props { var age: Int = 0 private set } TFUUFSHFUUFS
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43. &OVN
44. &OVN
    
    8IFO enum class BlendMode { OPAQUE, TRANSPARENT, FADE, ADD } fun blend(b: BlendMode) { when (b) { BlendMode.OPAQUE -> opaque() BlendMode.TRANSPARENT -> transparent() BlendMode.FADE -> fade() BlendMode.ADD -> add() } } public final class EnumTestKt$WhenMappings { // $FF: synthetic field public static final int[] $EnumSwitchMapping$0 = new int[BlendMode.values().length]; static { $EnumSwitchMapping$0[BlendMode.OPAQUE.ordinal()] = 1; $EnumSwitchMapping$0[BlendMode.TRANSPARENT.ordinal()] = 2; $EnumSwitchMapping$0[BlendMode.FADE.ordinal()] = 3; $EnumSwitchMapping$0[BlendMode.ADD.ordinal()] = 4; } } public final class EnumTestKt { public static final void blend(@NotNull BlendMode b) { Intrinsics.checkParameterIsNotNull(b, "b"); switch(EnumTestKt$WhenMappings.$EnumSwitchMapping$0[b.ordinal()]) { case 1: opaque(); break; case 2: transparent(); break; case 3: fade(); break; case 4: add(); } } }
45. &OVN
    
    8IFO enum class BlendMode { OPAQUE, TRANSPARENT, FADE, ADD } fun blend(b: BlendMode) { when (b) { BlendMode.OPAQUE -> opaque() BlendMode.TRANSPARENT -> transparent() BlendMode.FADE -> fade() BlendMode.ADD -> add() } } fun blend2(b: BlendMode) { when (b) { BlendMode.FADE -> fade() BlendMode.ADD -> add() BlendMode.TRANSPARENT -> transparent() BlendMode.OPAQUE -> opaque() } } public final class EnumTestKt$WhenMappings { // $FF: synthetic field public static final int[] $EnumSwitchMapping$0 = new int[BlendMode.values().length]; // $FF: synthetic field public static final int[] $EnumSwitchMapping$1; static { $EnumSwitchMapping$0[BlendMode.OPAQUE.ordinal()] = 1; $EnumSwitchMapping$0[BlendMode.TRANSPARENT.ordinal()] = 2; $EnumSwitchMapping$0[BlendMode.FADE.ordinal()] = 3; $EnumSwitchMapping$0[BlendMode.ADD.ordinal()] = 4; $EnumSwitchMapping$1 = new int[BlendMode.values().length]; $EnumSwitchMapping$1[BlendMode.FADE.ordinal()] = 1; $EnumSwitchMapping$1[BlendMode.ADD.ordinal()] = 2; $EnumSwitchMapping$1[BlendMode.TRANSPARENT.ordinal()] = 3; $EnumSwitchMapping$1[BlendMode.OPAQUE.ordinal()] = 4; } }
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49. 3BOHFT
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    GPSMPPQ fun testForLoop1() { for (i in 0..10) {} } fun testForLoop2() { for (index in 0 until 10) { } } fun testForLoop3() { repeat(10) {} } fun testForLoop4() { (0..10).forEach {} } public final class RangesTestKt { public static final void testForLoop1() { int var0 = 0; for(byte var1 = 10; var0 <= var1; ++var0) { } } public static final void testForLoop2() { int var0 = 0; for(byte var1 = 10; var0 < var1; ++var0) { } } public static final void testForLoop3() { byte var0 = 10; int var1 = 0; for(byte var2 = var0; var1 < var2; ++var1) { } } public static final void testForLoop4() { byte var0 = 0; Iterable $receiver$iv = (Iterable)(new IntRange(var0, 10)); int element$iv; for(Iterator var1 = $receiver$iv.iterator(); var1.hasNext(); element$iv = ((IntIterator)var1).nextInt()) { } } }
51. 3BOHFT
    
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53. -B[Z
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54. class MainActivity : AppCompatActivity() { private var mWelcomeTextView: TextView? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) mWelcomeTextView = findViewById(R.id.msgView) as TextView } } :PVS
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55. class MainActivity : AppCompatActivity() { private lateinit var mWelcomeTextView: TextView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) mWelcomeTextView = findViewById(R.id.msgView) as TextView } } 3FNPWJOH
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56. class MainActivity : AppCompatActivity() { private val mWelcomeTextView: TextView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // Where am I????? // mWelcomeTextView = // findViewById(R.id.msgView) as TextView } } *G
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57. class MainActivity : AppCompatActivity() { private val messageView : TextView by lazy { // following code will be executed at first access findViewById(R.id.message_view) as TextView } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) } fun onSayHello() { messageView.text = "Hello" } } -B[Z
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62. class Demo { val myName : String by lazy { "John" } } -B[Z
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63. class Demo { val myName : String by lazy { getNameFromPreference() } } initializer delegate
64. myName Lazy<T> getValue() { getNameFromPreference() } initializer class Demo { val myName : String by lazy { getNameFromPreference() } }
65. myName Lazy<T> getValue() UNINITIALIZED_VALUE { getNameFromPreference() } initializer class Demo { val myName : String by lazy { getNameFromPreference() } }
66. myName Lazy<T> getValue() “John” { getNameFromPreference() } initializer class Demo { val myName : String by lazy { getNameFromPreference() } }
67. myName Lazy<T> getValue() “John” initializer null class Demo { val myName : String by lazy { getNameFromPreference() } }
68. class MainActivity : AppCompatActivity() { private val messageView : TextView by lazy { // I’ll be initialized lazily at first access findViewById(R.id.message_view) as TextView } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) } fun onSayHello() { messageView.text = "Hello" } } #BDL
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69. val messageView: TextView by lazy { findViewById(R.id.message_view) as TextView } property delegate ↟MB[Z
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72. interface A { fun hello(): String } class B : A { override fun hello() = "Hello!!" } class C : A by B() $MBTT
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73. public interface A { @NotNull String hello(); } public final class B implements A { @NotNull public String hello() { return "Hello!!"; } } public final class C implements A { // $FF: synthetic field private final B $$delegate_0 = new B(); @NotNull public String hello() { return this.$$delegate_0.hello(); } } 4BNQMF
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76. fun String.hello() : String { return "Hello, $this" } fun main(args: Array<String>) { val whom = "cwdoh" println(whom.hello()) } // Result Hello, cwdoh &YUFOTJPO
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79. class Person { fun hello() { println("hello!") } } fun Person.hello() { println("উ֞?!!") } fun main(args: Array<String>) { Person().hello() } // Result hello! 3VMF
    
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80. class D { fun bar() { println("D.bar()") } } class C { fun baz() { println("C.bar()") } fun D.foo() { bar() // calls D.bar baz() // calls C.baz } fun caller(d: D) { d.foo() } } 3VMF
    
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82. data class Length(var centimeters: Int = 0) var Length.meters: Float get() { return centimeters / 100.0f } set(meters: Float) { this.centimeters = (meters * 100.0f).toInt() } &YUFOTJPO
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83. &YUFOTJPO
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    JOUFSGBDF data class Length(var centimeters: Int = 0) var Length.meters: Float get() { return centimeters / 100.0f } set(meters: Float) { this.centimeters = (meters * 100.0f).toInt() } public final class Length { private int centimeters; ... } public final class ExtensionsKt { public static final float getMeters( @NotNull Length $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); return (float)$receiver.getCentimeters() / 100.0F; } public static final void setMeters( @NotNull Length $receiver, float meters) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); $receiver.setCentimeters((int)(meters * 100.0F)); } ... }
84. fun Any?.toString(): String { if (this == null) return “null" return toString() } /VMMBCMF
    SFDFJWFS public final class SimpleClassKt { @NotNull public static final String toString(@Nullable Object $receiver) { return $receiver == null? "null":$receiver.toString(); } }
85. fun Any?.toString(): String { println("Extension is called.") if (this == null) return "null" return toString() } fun main(args: Array<String>) { val var1 : Any? = null println(var1.toString()) val str1 : String? = null println(str1.toString()) var str2 : String? = "hello" println(str2.toString()) var str3 : String = "world" println(str3.toString()) } $"65*0/
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     public final class SimpleClassKt { @NotNull public static final String toString(@Nullable Object $receiver) { String var1 = "Extension is called."; System.out.println(var1); return $receiver == null?"null":$receiver.toString(); } public static final void main(@NotNull String[] args) { Intrinsics.checkParameterIsNotNull(args, “args"); Object var1 = null; String str1 = toString(var1); System.out.println(str1); str1 = (String)null; String str2 = toString(str1); System.out.println(str2); str2 = "hello"; String str3 = toString(str2); System.out.println(str3); str3 = "world"; String var5 = str3.toString(); System.out.println(var5); } } Extension is called. null Extension is called. null Extension is called. hello world
86. JOMJOF
87. JOMJOF
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88. OPJOMJOF
    GVODUJPO fun sing() { println("We will we will rock you") println("(Sing it!)") println("We will we will rock you") } fun beatbox() { println("pv zk bschk pv zk") } fun ensemble() { sing() beatbox() sing() beatbox() } public final class SimpleClassKt { public static final void sing() { String var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); } public static final void beatbox() { String var0 = "pv zk bschk pv zk"; System.out.println(var0); } public static final void ensemble() { sing(); beatbox(); sing(); beatbox(); } }
89. JOMJOF
    GVODUJPO fun sing() { println("We will we will rock you") println("(Sing it!)") println("We will we will rock you") } fun beatbox() { println("pv zk bschk pv zk") } fun ensemble() { sing() beatbox() sing() beatbox() } public final class SimpleClassKt { public static final void sing() { String var1 = "We will we will rock you"; … } public static final void beatbox() { … } public static final void ensemble() { String var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); beatbox(); var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); beatbox(); } }
90. fun log(message: () -> String) { println(message()) } fun test() { log { "Lorem ipsum dolor sit amet, consectetur ..." } } -PHHJOH public final class SimpleClassKt { public static final void log(@NotNull Function0 message) { Intrinsics.checkParameterIsNotNull(message, "message"); Object var1 = message.invoke(); System.out.println(var1); } public static final void test() { log((Function0)null.INSTANCE); } }
91. inline fun trace(message: String) {} fun doSomething() { print("I'm doing something!") trace("doSomething() is doing something!") } FNQUZ
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    GVODUJPO public final class SimpleClassKt { public static final void trace(@NotNull String message) { Intrinsics.checkParameterIsNotNull(message, "message"); } public static final void doSomething() { String var0 = "I'm doing something!"; System.out.print(var0); var0 = "doSomething() is doing something!"; } }
92. JOMJOF
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93. &OVN
    
    8IFO inline class Color(private val c: Int) { val a get() = (c shr 24) and 0xff val r get() = (c shr 16) and 0xff val g get() = (c shr 8) and 0xff val b get() = (c ) and 0xff } fun test() { val a = Color(0x7f_10_20_30) val b = Color(0x7f_30_20_10) println(a == b) println(a.equals(b)) } public final class InlineClassKt { public static final void test() { int a = Color.constructor-impl(2131763248); int b = Color.constructor-impl(2133860368); boolean var2 = Intrinsics.areEqual( Color.box-impl(a), Color.box-impl(b)); System.out.println(var2); var2 = Color.equals-impl(a, Color.box-impl(b)); System.out.println(var2); } }
94. "SSBZ
95. *OJUJBMJ[JOH
    "SSBZ var arr1 = intArrayOf(0, 1, 2) var arr2 = arrayOf(0, 1, 2) var arr3 = IntArray(3) { it } @NotNull private static int[] arr1 = new int[]{0, 1, 2}; @NotNull private static Integer[] arr2 = new Integer[]{0, 1, 2}; @NotNull private static int[] arr3; static { int size$iv = 3; int[] result$iv = new int[size$iv]; int i$iv = 0; for(int var3 = result$iv.length; i$iv < var3; result$iv[i$iv] = i$iv++) { } arr3 = result$iv; }
96. -BNCEB
97. JOMJOF
    GVODUJPO public class Widget { public interface Listener { void onEvent(Widget widget); } private int listenerCount = 0; public int getListenerCount() { return listenerCount; } public void addListener(Listener listener) {} public void removeListener(Listener listener) {} } val w = Widget() val listener = { widget: Widget -> println("Listened to $widget") } w.addListener(listener) println(w.listenerCount) w.removeListener(listener) println(w.listenerCount)
98. JOMJOF
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99. $PSPVUJOF
100. $PSPVUJOF
101. $PSPVUJOF
104. 4VTQFOE
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105. fun fetchUserDetail(id: String) { val token = auth() val user = getUser(token, id) updateUserData(user) } BVUI Waaaaa~~it HFU6TFS VQEBUF6TFS%BUB 8BBBBB__JU
     
106. fun fetchUserDetail(id: String) { auth { token -> getUser(token) { updateUserData(it) } } } BVUI HFU6TFS VQEBUF6TFS%BUB
107. suspend fun fetchUserDetail(id: String) { val token = auth() val user = getUser(token, id) updateUserData(user) } suspend BVUI *%-&
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108. fun plusOne(initial: Int) : Int { val ONE = 1 var result = initial result += ONE return result } 4UBUF
109. )PX
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110. suspend fun fetchUserDetail(id: String) { val token = auth() val user = getUser(token, id) updateUserData(user) } }
111. suspend fun fetchUserDetail(id: String) { // ... switch (label) { case 0: val token = auth() case 1: val user = getUser(token, id) case 2: updateUserData(user) } }
112. fun fetchUserDetail(id: String) { // ... switch (label) { case 0: val token = auth() case 1: val user = getUser(token, id) case 2: updateUserData(user) } } -BCFMJOH
113. fun fetchUserDetail(id: String, cont: Continuation) { switch ( label) { case 0: auth( ) case 1: getUser(token, id ) case 2: … } } val sm = object : CoroutineImpl { ... } sm. sm , sm 4UBUF
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114. fun fetchUserDetail(id: String, cont: Contiunation) { val sm = object : CoroutineImpl { ... } switch (sm.label) { case 0: auth(sm) case 1: getUser(token, id, sm) case 2: … } } $POUJOVBUJPO
115. fun fetchUserDetail(id: String, cont: Contiunation) { val sm = object : CoroutineImpl { ... } switch (sm.label) { case 0: sm.id = id sm.label = 1 auth(sm) … } } 4BWF
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116. fun fetchUserDetail(id: String, cont: Contiunation) { val sm = object : CoroutineImpl { ... } switch (sm.label) { … case 1: val id = sm.id val token = sm.result as String sm.label = 2 getUser(token, id, sm) … } 3FTUPSF
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117. fun fetchUserDetail(id: String, cont: Contiunation) { val sm = object : CoroutineImpl { fun resume(...) { fetchUserDetail(null, this) } } switch (sm.label) { case 0: … } } 3FTVNF
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118. fun fetchUserDetail(id: String, cont: Contiunation) { val sm = cont as? ThisSM ?: object : CoroutineImpl { fun resume(...) { fetchUserDetail(null, this) } } switch (sm.label) { case 0: … } } $POUJOVBUJPO
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119. https://goo.gl/2Tyx4B (eng.) https://goo.gl/H9iih9 (kor.)
120. UIBOL
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