Kotlin Fest 2019: Kotlin型実践入門

KotlinではJavaにはない様々な型に関する機能が追加されたので、それらの解説

- Smart Casts
- Any、Unit、Nothing
- ジェネリクス
- Sealed class
- 関数型

Transcript

1. Kotlin Fest
   2019
   ࠤ౻ ൏ / Sato Shun
   
   Twitter: @stsn_jp
   
   GitHub: satoshun
   Kotlinܕ࣮ફೖ໳
   

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2. ֓ཁ
   • KotlinͰ͸Javaʹ͸ͳ͍༷ʑͳܕʹؔ͢Δػೳ͕௥Ճ͞Εͨ
   ͷͰɺͦΕΒͷղઆ
   
   • ॳֶऀ޲͚ͷ಺༰ʹͳ͓ͬͯΓ·͢
   

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3. ໨࣍
   • Smart Casts
   
   • AnyɺUnitɺNothing
   
   • δΣωϦΫε
   
   • Sealed class
   
   • ؔ਺ܕ
   

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4. •Smart Casts
   • AnyɺUnitɺNothing
   
   • δΣωϦΫε
   
   • Sealed class
   
   • ؔ਺ܕ
   

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5. Smart Casts
   • ifࣜɺwhenࣜɺisɺasͳͲͷ࣮ߦޙʹɺ໌ࣔతʹܕΩϟετ
   ͠ͳͯ͘΋ɺܕΛਪ࿦ͯ͘͠ΕΔ
   
   • flow-sensitive typing (flow typing)ͱݺ͹ΕΔܕγεςϜ
   

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6. Smart Casts
   • ifࣜɺwhenࣜɺisɺasͳͲͷ࣮ߦޙʹɺ໌ࣔతʹܕΩϟετ
   ͠ͳͯ͘΋ɺܕΛਪ࿦ͯ͘͠ΕΔ
   
   • flow-sensitive typing (flow typing)ͱݺ͹ΕΔܕγεςϜ
   
   • ৑௕ͳܕΩϟετΛܰݮ͢Δ
   
   • ಈతܕ෇͚ݴޠͷμοΫλΠϐϯάͷΑ͏ͳॻ͖৺஍
   
   • https://en.wikipedia.org/wiki/Flow-sensitive_typing
   

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7. if (obj is String) {
   a
   print((obj as String).length)
   }
   a
   if (obj !is String) return
   print((obj as String).length)
   when (obj) {
   aa
   is Int -> print((obj as Int) + 1)
   is String -> print((obj as String).length + 1)
   is IntArray -> print((obj as IntArray).sum() + 1)
   }
   a
   

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8. if (obj is String) {
   a
   print(obj.length)
   }
   a
   if (obj !is String) return
   print((obj as String).length)
   when (obj) {
   aa
   is Int -> print((obj as Int) + 1)
   is String -> print((obj as String).length + 1)
   is IntArray -> print((obj as IntArray).sum() + 1)
   }
   a
   

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9. if (obj is String) {
   a
   print(obj.length)
   }
   a
   if (obj !is String) return
   print(obj.length)
   when (obj) {
   aa
   is Int -> print((obj as Int) + 1)
   is String -> print((obj as String).length + 1)
   is IntArray -> print((obj as IntArray).sum() + 1)
   }
   a
   

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10. if (obj is String) {
    a
    print(obj.length)
    }
    a
    if (obj !is String) return
    print(obj.length)
    when (obj) {
    a
    is Int -> print(obj + 1)
    is String -> print(obj.length + 1)
    is IntArray -> print(obj.sum() + 1)
    }
    a
    

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11. if (hoge() && obj is Int) {
    a
    (obj as Int).toLong()
    }
    a
    if (obj is String && obj is Int) {
    a
    (obj as String).length
    (obj as Int).toLong()
    }
    a
    

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12. if (hoge() && obj is Int) {
    a
    obj.toLong()
    }
    a
    if (obj is String && obj is Int) {
    a
    (obj as String).length
    (obj as Int).toLong()
    }
    a
    

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13. if (hoge() && obj is Int) {
    a
    obj.toLong()
    }
    a
    if (obj is String && obj is Int) {
    a
    obj.length
    obj.toLong()
    }
    a
    

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14. class Hoge {
    a
    private var obj: Any = "a"
    fun test() {
    a
    if (obj is String) {
    a
    print((obj as String).length)
    }
    a
    }
    a
    }
    a
    

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15. class Hoge {
    a
    private var obj: Any = "a"
    fun test() {
    a
    if (obj is String) {
    a
    print(obj.length)
    }
    a
    }
    a
    }
    a
    

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16. class Hoge {
    a
    private var obj: Any = "a"
    fun test() {
    a
    if (obj is String) {
    a
    print(obj.length)
    }
    a
    }
    a
    }
    a
    ❌
    

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17. class Hoge {
    a
    private var obj: Any = "a"
    fun test() {
    a
    val obj = obj
    if (obj is String) {
    a
    print(obj.length)
    }
    a
    }
    a
    }
    a
    

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18. class Hoge {
    a
    private var obj: Any = "a"
    fun test() {
    a
    obj.let {
    a
    if (it is String) {
    a
    print(it.length)
    }
    a
    }
    a
    }
    a
    }
    a
    

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19. val strs: List? = …
    a
    if (!strs.isNullOrEmpty()) {
    a
    println(strs!!.size)
    }
    a
    

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20. val strs: List? = …
    a
    if (!strs.isNullOrEmpty()) {
    a
    println(strs.size)
    }
    a
    

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21. Contracts
    • Smart CastsΛ֦ு͢Δػೳ
    
    • ؔ਺ݺͼग़͠ͷ݁ՌΛ΋ͱʹɺSmart Casts͢Δ͜ͱ͕ग़དྷ
    Δ
    

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22. public inline fun Collection?.isNullOrEmpty():
    Boolean {
    a
    contract {
    a
    returns(false) implies (this@isNullOrEmpty != null)
    }
    a
    return this == null || this.isEmpty()
    }
    a
    

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23. public inline fun Collection?.isNullOrEmpty():
    Boolean {
    a
    contract {
    a
    returns(false) implies (this@isNullOrEmpty != null)
    }
    a
    return this == null || this.isEmpty()
    }
    a
    

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24. public inline fun Collection?.isNullOrEmpty():
    Boolean {
    a
    contract {
    a
    returns(false) implies (this@isNullOrEmpty != null)
    }
    a
    return this == null || this.isEmpty()
    }
    a
    

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25. public inline fun Collection?.isNullOrEmpty():
    Boolean {
    a
    contract {
    a
    returns(false) implies (this@isNullOrEmpty != null)
    }
    a
    return this == null || this.isEmpty()
    }
    a
    

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26. val strs: List? = …
    a
    if (!strs.isNullOrEmpty()) {
    a
    println(strs!!.size)
    }
    a
    

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27. val strs: List? = …
    a
    if (!strs.isNullOrEmpty()) {
    a
    println(strs.size)
    }
    a
    

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28. fun assertTrue(actual: Boolean, message: String? = null) {
    a
    contract { returns() implies actual }
    a
    return asserter.assertTrue(message ?: "Expected value to
    be true.", actual)
    }
    a
    

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29. fun assertTrue(actual: Boolean, message: String? = null) {
    a
    contract { returns() implies actual }
    a
    return asserter.assertTrue(message ?: "Expected value to
    be true.", actual)
    }
    a
    

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30. fun assertTrue(actual: Boolean, message: String? = null) {
    a
    contract { returns() implies actual }
    a
    return asserter.assertTrue(message ?: "Expected value to
    be true.", actual)
    }
    a
    assertTrue(obj != null)
    print(obj!!.length)
    

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31. fun assertTrue(actual: Boolean, message: String? = null) {
    a
    contract { returns() implies actual }
    a
    return asserter.assertTrue(message ?: "Expected value to
    be true.", actual)
    }
    a
    assertTrue(obj != null)
    print(obj.length)
    

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32. fun assertFalse(actual: Boolean, message: String? = null) {
    contract { returns() implies (!actual) }
    return asserter.assertTrue(message ?: "Expected value to
    be false.", !actual)
    }
    assertFalse(obj == null)
    print(obj.length)
    

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33. fun assertFalse(actual: Boolean, message: String? = null) {
    contract { returns() implies (!actual) }
    return asserter.assertTrue(message ?: "Expected value to
    be false.", !actual)
    }
    assertFalse(obj == null)
    print(obj.length)
    

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34. public inline fun run(block: () -> R): R {
    a
    contract {
    a
    callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    a
    return block()
    }
    a
    

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35. public inline fun run(block: () -> R): R {
    a
    contract {
    a
    callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    a
    return block()
    }
    a
    

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36. public inline fun run(block: () -> R): R {
    a
    contract {
    a
    callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    a
    return block()
    }
    a
    var s: String? = null
    a
    run {
    a
    s = ""
    a
    }
    a
    println(s!!)
    a
    

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37. public inline fun run(block: () -> R): R {
    a
    contract {
    a
    callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    a
    return block()
    }
    a
    val s: String
    a
    run {
    a
    s = ""
    a
    }
    a
    println(s)
    a
    

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38. fun checkObj(obj: Any?): Boolean {
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj!!.javaClass
    }
    a
    

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39. fun checkObj(obj: Any?): Boolean {
    a
    contract {
    a
    returns(true) implies (obj != null)
    }
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj!!.javaClass
    }
    a
    

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40. fun checkObj(obj: Any?): Boolean {
    a
    contract {
    a
    returns(true) implies (obj != null)
    }
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj!!.javaClass
    }
    a
    

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41. fun checkObj(obj: Any?): Boolean {
    a
    contract {
    a
    returns(true) implies (obj != null)
    }
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj!!.javaClass
    }
    a
    

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42. fun checkObj(obj: Any?): Boolean {
    a
    contract {
    a
    returns(true) implies (obj != null)
    }
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj.javaClass
    }
    a
    

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43. @UseExperimental(ExperimentalContracts::class)
    fun checkObj(obj: Any?): Boolean {
    a
    contract {
    a
    returns(true) implies (obj != null)
    }
    a
    return obj != null
    }
    a
    if (checkObj(obj)) {
    a
    obj.javaClass
    }
    a
    

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44. • Smart Casts
    
    •AnyɺUnitɺNothing
    • δΣωϦΫε
    
    • Sealed class
    
    • ؔ਺ܕ
    

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45. Anyܕ
    • ͢΂ͯͷKotlinͷΫϥεͷεʔύʔΫϥε
    
    • ϧʔτΫϥε
    
    • Javaͷ৔߹ɺjava.lang.Object͕ϧʔτΫϥε
    

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46. Anyܕ
    • JavaͷObjectͱҧ͏఺͸Ͳ͔͜ʁ
    
    • waitɺnotifyϝιου͕࢖͑ͳ͍
    
    • ໌ࣔతʹjava.lang.ObjectܕʹΩϟετ͢Ε͹ݺͼग़ͤΔ
    
    • getClassϝιου͕֦ுؔ਺ʹ
    
    • public inline val T.javaClass: Class
    
    • cloneɺfinalizeϝιου
    

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47. val s = ""
    s.notify()
    

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48. val s = ""
    (s as Object).notify()
    

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49. Unitܕ
    • JavaͰ͍͏ͱ͜ΖͷvoidΛදݱ͢ΔΫϥε
    
    • ฦΓ஋͕ۭͰ͋Δ͜ͱΛද͢
    

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50. fun empty() {
    a
    }
    a
    empty()
    

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51. fun empty(): Unit {
    a
    }
    a
    empty()
    

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52. fun empty(): Unit {
    a
    }
    a
    val e = empty()
    println(e)
    

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53. fun empty() {
    a
    }
    a
    val e = empty()
    println(e)
    

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54. Nothingܕ
    • ͢΂ͯͷKotlinͷΫϥεͷαϒΫϥε
    
    • ஋͕ଘࡏ͠ͳ͍͜ͱΛࣔ͢
    
    • ਖ਼ৗऴྃ͢Δ͜ͱ͕ͳ͍ؔ਺ͷฦΓ஋ʹ࢖͑Δ
    

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55. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail() {
    a
    throw RuntimeException()
    }
    a
    

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56. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail() {
    a
    throw RuntimeException()
    }
    a
    val name = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    

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57. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail() {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    

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58. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail() {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    

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59. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail() {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println((name as String).length)
    

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60. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println((name as String).length)
    

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61. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println((name as String).length)
    

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62. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name: Any = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println((name as String).length)
    

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63. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name: String = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println((name as String).length)
    

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64. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name: String = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println(name.length)
    

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65. fun getName(): String {
    a
    return "name"
    }
    a
    fun fail(): Nothing {
    a
    throw RuntimeException()
    }
    a
    val name = if (isFriend()) {
    a
    getName()
    }
    a
    else {
    a
    fail()
    }
    a
    println(name.length)
    

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66. fun test(any: Any): String {
    a
    when (any) {
    a
    is Int -> return "int"
    else -> fail()
    }
    a
    return "error"
    }
    a
    

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67. fun test(any: Any): String {
    a
    when (any) {
    a
    is Int -> return "int"
    else -> fail()
    }
    a
    return "error"
    }
    a
    NothingܕͳͷͰɺ͜ͷݺͼग़͠͸ਖ਼ৗʹऴྃ͠ͳ͍
    ͜ͷelse͸ඞࣦͣഊ͢Δ
    

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68. fun test(any: Any): String {
    a
    when (any) {
    a
    is Int -> return "int"
    else -> fail()
    }
    a
    }
    a
    

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69. // ඪ४ؔ਺
    public inline fun TODO(): Nothing = throw
    NotImplementedError()
    // KotlinTest
    fun fail(msg: String): Nothing = throw
    Failures.failure(msg)
    

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70. // Kotlin/kotlinx.collections.immutable
    internal companion object {
    internal val EMPTY = TrieNode(0, emptyArray())
    }
    // airbnb/MvRx
    object Uninitialized : Async(complete = false,
    shouldLoad = true), Incomplete
    

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71. fun test2() {
    a
    while (true) {
    a
    println(".")
    }
    a
    }
    a
    

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72. fun test2(): Nothing {
    a
    while (true) {
    a
    println(".")
    }
    a
    }
    a
    

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73. Nothing?ܕ
    • Nothing?ܕ΋ଘࡏ͢Δ
    
    • Nothing͸஋ͱͯ͠ଘࡏ͠ͳ͍ͷͰɺnullͷΈΛڐՄ͢Δ
    

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74. // kotlintest/kotlintest
    interface Show {
    a
    fun supports(a: Any?): Boolean
    fun show(a: A): String
    }
    a
    object NullShow : Show {
    a
    override fun supports(a: Any?): Boolean = a == null
    override fun show(a: Nothing?): String = ""
    }
    a
    

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75. • Smart Casts
    
    • AnyɺUnitɺNothing
    
    •δΣωϦΫε
    • Sealed class
    
    • ؔ਺ܕ
    

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76. δΣωϦΫε
    • ෼ࢄΞϊςʔγϣϯʢvariance annotationʣ
    
    • outɺinम০ࢠ
    
    • એݴଆมੑ: declaration-site variance
    
    • where
    
    • reified
    
    • ֦ுؔ਺ + δΣωϦΫε
    

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77. ෼ࢄΞϊςʔγϣϯ
    • out - ڞม: covariance
    
    • in - ൓ม: contravariance
    
    • ࢦఆͳ͠: ෆม: invariance
    

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78. ڞมɺ൓มɺෆม
    • Number

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79. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    

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80. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    

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81. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    
    • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ
    

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82. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    
    • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ
    

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83. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    
    • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ
    
    • Aɺ A͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ
    

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84. ڞมɺ൓มɺෆม
    • Number
    • A ͷ৔߹ɺA͸ڞมͰ͋Δ
    
    • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ
    
    • Aɺ A͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ
    

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85. // ڞม
    val a: A = A()
    a
    val b: A = a
    

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86. // ڞม
    val a: A = A()
    a
    val b: A = a
    // ൓ม
    val a: A = A()
    a
    val b: A = a
    

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87. // ڞม
    val a: A = A()
    a
    val b: A = a
    // ൓ม
    val a: A = A()
    a
    val b: A = a
    // ෆม
    val a: A = A()
    a
    

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88. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    

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89. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    

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90. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    

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91. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    ❌
    

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92. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    ❌
    

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93. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    ❌
    

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94. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    ❌
    

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95. interface Mapper {
    a
    fun map(s: String): T
    }
    a
    class IntMapper : Mapper {
    a
    override fun map(s: String): Int = s.toInt()
    }
    a
    fun hoge(mapper: Mapper) {
    a
    mapper.map("10")
    }
    a
    val mapper = IntMapper()
    hoge(mapper)
    

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96. ListͱMutableList
    public interface List : Collection
    
    public interface MutableList : List, …
    
    

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97. ListͱMutableList
    public interface List : Collection
    
    public interface MutableList : List, …
    
    • List͸outम০ࢠ͕෇͍͍ͯΔͷͰɺڞม
    
    • MutableList͸Կ΋෇͍͍ͯͳ͍ͷͰɺෆม
    

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98. val strs: List = listOf("a", “b")
    

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99. val strs: List = listOf("a", “b")
    val anys: List = strs
    

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100. val strs: List = listOf("a", “b")
     val anys: List = strs
     val a: Any = anys[0]
     

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101. val strs: List = listOf("a", “b")
     val anys: List = strs
     val a: Any = anys[0]
     val a2: Any? = anys2.getOrNull(1)
     

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102. val strs: List = listOf("a", “b")
     val anys: List = strs
     val a: Any = anys[0]
     val a2: Any? = anys2.getOrNull(1)
     

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103. val strs: MutableList = mutableListOf("a", "b")
     

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104. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     

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105. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     anys.add(10)
     

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106. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     anys.add(10)
     

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107. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     anys.add(10)
     val str: String = strs.last()
     

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108. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     anys.add(10)
     val str: String = strs.last()
     ❌
     

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109. val strs: MutableList = mutableListOf("a", "b")
     val anys: MutableList = strs
     anys.add(10)
     val str: String = strs.last()
     

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110. PECS
     • Producer Extends Consumer Super
     
     • Producer͸readͷੑ࣭Λ࣋ͭ
     
     • Consumer͸writeͷੑ࣭Λ࣋ͭ
     
     • List͸Producerͷੑ࣭ͷΈΛ࣋ͭͷͰɺExtends = out ڞมʹ
     ग़དྷΔ
     
     • MutableList͸ProducerͱConsumerͷੑ࣭Λ࣋ͭͷͰɺෆม
     

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111. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺
     • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ
     ͍
     

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112. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺
     • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ
     ͍
     
     • fun hoge(t: T) {…}
     

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113. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺
     • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ
     ͍
     
     • fun hoge(t: T) {…}
     
     • 2ͭҎ্ͷ্քΛ࣋ͭ৔߹͸Ͳ͏͢Ε͹Α͍͔ʁ
     
     • ྫ͑͹ɺActivity͔ͭOnClickListenerΛ࣋ͭܕΛड͚ೖΕΔܕ
     ม਺Λఆ͍ٛͨ͠
     

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114. class OnClickActivity() : Activity(), OnClickListener
     

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115. class OnClickActivity() : Activity(), OnClickListener
     fun setClick(activity: OnClickActivity) {
     a
     }
     a
     

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116. class OnClickActivity() : Activity(), OnClickListener
     fun setClick(activity: OnClickActivity) {
     a
     }
     a
     val activity = OnClickActivity()
     setClick(activity)
     

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117. class OnClickActivity() : Activity(), OnClickListener
     fun setClick(activity: OnClickActivity) {
     a
     }
     a
     val activity = OnClickActivity()
     setClick(activity)
     class OnClickActivity2() : Activity(), OnClickListener
     

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118. class OnClickActivity() : Activity(), OnClickListener
     fun setClick(activity: OnClickActivity) {
     a
     }
     a
     val activity = OnClickActivity()
     setClick(activity)
     class OnClickActivity2() : Activity(), OnClickListener
     val activity2 = OnClickActivity2()
     setClick(activity2)
     

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119. class OnClickActivity() : Activity(), OnClickListener
     fun setClick(activity: OnClickActivity) {
     a
     }
     a
     val activity = OnClickActivity()
     setClick(activity)
     class OnClickActivity2() : Activity(), OnClickListener
     val activity2 = OnClickActivity2()
     setClick(activity2)
     ❌
     

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120. fun setClick(activity: OnClickActivity) {
     a
     }
     a
     

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121. fun setClick(activity: T)
     

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122. fun setClick(activity: T)
     where T : Activity,
     T : OnClickListener {
     a
     }
     a
     

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123. fun setClick(activity: T)
     where T : Activity,
     T : OnClickListener {
     a
     }
     a
     val activity = OnClickActivity()
     setClick(activity)
     

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124. fun setClick(activity: T)
     where T : Activity,
     T : OnClickListener {
     }
     val activity = OnClickActivity()
     setClick(activity)
     val activity2 = OnClickActivity2()
     setClick(activity2)
     

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125. internal abstract class NIOSocketImpl(
     override val channel: S,
     val selector: SelectorManager,
     val pool: ObjectPool?
     ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope
     where S : java.nio.channels.ByteChannel, S :
     java.nio.channels.SelectableChannel
     Ktor
     

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126. internal abstract class NIOSocketImpl(
     override val channel: S,
     val selector: SelectorManager,
     val pool: ObjectPool?
     ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope
     where S : java.nio.channels.ByteChannel, S :
     java.nio.channels.SelectableChannel
     Ktor
     

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127. internal abstract class NIOSocketImpl(
     override val channel: S,
     val selector: SelectorManager,
     val pool: ObjectPool?
     ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope
     where S : java.nio.channels.ByteChannel, S :
     java.nio.channels.SelectableChannel
     internal class DatagramSocketImpl(override val channel:
     DatagramChannel, selector: SelectorManager)
     : BoundDatagramSocket, ConnectedDatagramSocket,
     NIOSocketImpl(channel, selector,
     DefaultDatagramByteBufferPool)
     Ktor
     

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128. internal abstract class NIOSocketImpl(
     override val channel: S,
     val selector: SelectorManager,
     val pool: ObjectPool?
     ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope
     where S : java.nio.channels.ByteChannel, S :
     java.nio.channels.SelectableChannel
     internal class DatagramSocketImpl(override val channel:
     DatagramChannel, selector: SelectorManager)
     : BoundDatagramSocket, ConnectedDatagramSocket,
     NIOSocketImpl(channel, selector,
     DefaultDatagramByteBufferPool)
     internal class SocketImpl(
     override val channel: S,
     private val socket: java.net.Socket,
     selector: SelectorManager
     ) : NIOSocketImpl(channel, selector, pool = null), Socket
     Ktor
     

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129. reified
     • ؔ਺಺͔Βܕม਺ʹΞΫηεग़དྷΔ
     
     • JavaͰ͸ܕม਺ʹϥϯλΠϜ࣌ʹΞΫηεͰ͖ͳ͍
     
     • Type Erasureͱݺ͹ΕΔݴޠ࢓༷ͷͨΊɺίϯύΠϧޙʹܕม਺͕
     ࡟আ͞ΕΔͨΊ
     

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130. inline fun hoge(obj: Any) {
     a
     println(T::class.java)
     a
     if (obj is T) {
     a
     println("obj is T")
     a
     }
     a
     }
     a
     

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131. inline fun hoge(obj: Any) {
     a
     println(T::class.java)
     a
     if (obj is T) {
     a
     println("obj is T")
     a
     }
     a
     }
     a
     

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132. inline fun hoge(obj: Any) {
     a
     println(T::class.java)
     a
     if (obj is T) {
     a
     println("obj is T")
     a
     }
     a
     }
     a
     

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133. ֦ுؔ਺ + δΣωϦΫε
     • Kotlinͷ֦ுؔ਺ͱδΣωϦΫεΛ૊Έ߹ΘͤΔͱΑΓॊೈʹ
     ܕม਺Λίϯτϩʔϧ͢Δ͜ͱ͕ग़དྷΔ
     

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134. class A(val value: T) {
     a
     fun isNull(): Boolean {
     a
     return value != null
     }
     a
     }
     a
     

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135. class A(val value: T) {
     a
     fun isNull(): Boolean {
     a
     return value != null
     }
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     

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136. class A(val value: T) {
     a
     fun isNull(): Boolean {
     a
     return value != null
     }
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     val a2: A = A(10)
     a
     a2.isNull()
     a
     

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137. class A(val value: T)
     a
     fun A.isNull(): Boolean {
     a
     return value != null
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     val a2: A = A(10)
     a
     a2.isNull()
     a
     

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138. class A(val value: T)
     a
     fun A.isNull(): Boolean {
     a
     return value != null
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     val a2: A = A(10)
     a
     a2.isNull()
     a
     

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139. class A(val value: T)
     a
     fun A.isNull(): Boolean {
     a
     return value != null
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     val a2: A = A(10)
     a
     a2.isNull()
     a
     

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140. class A(val value: T)
     a
     fun A.isNull(): Boolean {
     a
     return value != null
     a
     }
     a
     val a1: A = A(null)
     a
     a1.isNull()
     a
     val a2: A = A(10)
     a
     a2.isNull()
     a
     ❌
     

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141. • Smart Casts
     
     • AnyɺUnitɺNothing
     
     • δΣωϦΫε
     
     •Sealed class
     • ؔ਺ܕ
     

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142. Sealed class
     • ੍ݶ͞ΕͨαϒΫϥε֊૚ߏ଄Λ࡞Δ͜ͱ͕ग़དྷΔ
     
     • ಛघͳ༻్ͷabstract class
     

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143. abstract class Either
     object Left : Either()
     object Right : Either()
     when (obj) {
     a
     Left -> println("is Left")
     Right -> println("is Right")
     else -> println("else")
     }
     a
     

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144. sealed class Either
     object Left : Either()
     object Right : Either()
     when (obj) {
     a
     Left -> println("is Left")
     Right -> println("is Right")
     else -> println("else")
     }
     a
     

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145. sealed class Either
     object Left : Either()
     object Right : Either()
     when (obj) {
     a
     Left -> println("is Left")
     Right -> println("is Right")
     }
     a
     

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146. sealed͸classͰͷΈ༗ޮ
     • interfaceͩͱɺ༰қʹܧঝग़དྷͯ͠·͏ͨΊɺ੍໿ΛഁΕͯ
     ͠·͏
     

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147. public abstract class Either {
     private Either() {
     }
     // $FF: synthetic method
     public Either(DefaultConstructorMarker
     $constructor_marker) {
     this();
     }
     }
     

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148. public abstract class Either {
     private Either() {
     }
     // $FF: synthetic method
     public Either(DefaultConstructorMarker
     $constructor_marker) {
     this();
     }
     }
     

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149. • Smart Casts
     
     • AnyɺUnitɺNothing
     
     • δΣωϦΫε
     
     • Sealed class
     
     •ؔ਺ܕ
     

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150. ؔ਺ܕ
     • KotlinͰ͸ؔ਺ʢFunctionʣ͕ϑΝʔετΫϥεΦϒδΣΫτ
     
     • ม਺ɺؔ਺ͷҾ਺ɺ໭Γ஋ͳͲʹؔ਺ܕΛ࢖͏͜ͱ͕ग़དྷΔ
     

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151. ؔ਺ܕ
     • Function0 ~ Function22ͷ22Ҿ਺·Ͱͷؔ਺ΠϯλʔϑΣʔε
     ͱɺͦΕҎ্ͷҾ਺༻ͷɺFunctionNΠϯλʔϑΣʔε͕ఆٛ
     ͞Ε͍ͯΔ
     
     • ্هͷؔ਺ΠϯλʔϑΣʔεʹίϯύΠϧ࣌ʹม׵͞ΕΔ
     

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152. fun hoge(body: Function1) {
     a
     body(10)
     }
     a
     

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153. fun hoge(body: (Int) -> String) {
     a
     body(10)
     }
     a
     

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154. fun hoge(body: (Int) -> String) {
     a
     body(10)
     }
     a
     hoge { it.toString() }
     a
     

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155. fun add(a1: Int, a2: Int): Int {
     a
     return a1 + a2
     }
     a
     add
     add(10, 20)
     

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156. fun add(a1: Int, a2: Int): Int {
     a
     return a1 + a2
     }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     

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157. fun add(a1: Int, a2: Int): Int {
     a
     return a1 + a2
     }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     

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158. }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     fun ((P1, P2) -> R).curried(): (P1) -> (P2) ->
     R = { p1: P1 -> { p2: P2 -> this(p1, p2) } }
     a
     

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159. }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     fun ((P1, P2) -> R).curried(): (P1) -> (P2) ->
     R = { p1: P1 -> { p2: P2 -> this(p1, p2) } }
     a
     

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160. }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     fun ((P1, P2) -> R).curried(): (P1) -> (P2) ->
     R = { p1: P1 -> { p2: P2 -> this(p1, p2) } }
     a
     

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161. }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     fun ((P1, P2) -> R).curried(): (P1) -> (P2) ->
     R = { p1: P1 -> { p2: P2 -> this(p1, p2) } }
     a
     val curried = a.curried()
     

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162. }
     a
     add
     add(10, 20)
     val a: (Int, Int) -> Int = ::add
     a(10, 20)
     fun ((P1, P2) -> R).curried(): (P1) -> (P2) ->
     R = { p1: P1 -> { p2: P2 -> this(p1, p2) } }
     a
     val curried = a.curried()
     curried(10)(20)
     

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163. class A : (Int) -> Unit {
     a
     override fun invoke(p1: Int) {
     a
     println("call $p1")
     }
     a
     }
     a
     val a = A()
     a.invoke(10)
     

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164. class A : (Int) -> Unit {
     a
     override fun invoke(p1: Int) {
     a
     println("call $p1")
     }
     a
     }
     a
     val a = A()
     a(10)
     

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165. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     

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166. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     val a: (Number) -> Number = { it }
     a
     

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167. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     val a: (Number) -> Number = { it }
     a
     val a1: (Int) -> Number = a
     

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168. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     val a: (Number) -> Number = { it }
     a
     val a1: (Int) -> Number = a
     

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169. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     val a: (Number) -> Number = { it }
     a
     val a1: (Int) -> Number = a
     val a2: (Number) -> Any = a
     

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170. public interface Function1 : Function {
     public operator fun invoke(p1: P1): R
     }
     a
     val a: (Number) -> Number = { it }
     as
     val a1: (Int) -> Number = a
     val a2: (Number) -> Any = a
     

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171. SAMม׵
     • SAM?
     
     • Single Abstract Method
     
     • 1ͭͷந৅ϝιουΛ࣋ͭ
     
     • Kotlin͔ΒJavaఆٛͷSAMΛ࢖͏ͱ͖ʹɺϥϜμࣜͰ؆ܿʹ
     ॻ͘͜ͱ͕ग़དྷΔ
     

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172. public class SamTest {
     a
     public static void foo(Runnable a, Runnable b) {
     a
     }
     a
     }
     a
     fun test() {
     a
     SamTest.foo({}) {
     a
     }
     a
     }
     a
     

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173. public class SamTest {
     a
     public static void foo(Runnable a, Runnable b) {
     a
     }
     a
     }
     a
     fun test() {
     a
     SamTest.foo({}) {
     a
     }
     a
     }
     a
     public interface Runnable {
     public abstract void run();
     }
     

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174. public class SamTest {
     a
     public static void foo(Runnable a, Runnable b) {
     a
     }
     a
     }
     a
     fun test(r: Runnable) {
     a
     SamTest.foo(r) { }
     }
     a
     

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175. public class SamTest {
     a
     public static void foo(Runnable a, Runnable b) {
     a
     }
     a
     }
     a
     fun test(r: Runnable) {
     a
     SamTest.foo(r) { }
     }
     a
     ❌
     

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176. KotlinͷSAMม׵ͷ՝୊
     • ෳ਺ͷSAMΛҾ਺ʹऔΔ৔߹ɺ1ͭͰ΋࣮ମΛ࢖ͬͯ͠·͏
     ͱɺҙਤͨ͠ม׵͕ߦΘΕͳ͍
     

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177. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     a
     

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178. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     public static Observable combineLatest(
     ObservableSource extends T1> source1,
     ObservableSource extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     

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179. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     public static Observable combineLatest(
     ObservableSource extends T1> source1,
     ObservableSource extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     public interface ObservableSource {
     a
     void subscribe(@NonNull Observer super T> observer);
     }
     ˇ
     

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180. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     

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181. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     ❌
     

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182. // RxJava
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, BiFunction { n1, n2 ->
     n1 to n2
     })
     

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183. public static Observable combineLatest(
     ObservableSource extends T1> source1,
     ObservableSource extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     

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184. public static Observable combineLatest(
     Observable extends T1> source1,
     Observable extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     

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185. public static Observable combineLatest(
     Observable extends T1> source1,
     Observable extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, BiFunction { n1, n2 ->
     n1 to n2
     })
     

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186. public static Observable combineLatest(
     Observable extends T1> source1,
     Observable extends T2> source2,
     BiFunction super T1, ? super T2, ? extends R>
     combiner
     )
     a
     val o1 = Observable.just(1)
     val o2 = Observable.just(2)
     val combination = Observable
     .combineLatest(o1, o2, { n1, n2 ->
     n1 to n2
     })
     

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187. NewInference
     • kotlinͰ͸SAMม׵ͷ໰୊ʹରͯ͠ɺ৽͍͠ܕਪ࿦Λ։ൃͯ͠
     ͍Δ
     
     • ݱࡏɺexperimentalͷཱͪҐஔ͕ͩɺઃఆͰenableʹ͢Δ͜ͱ
     ͕Մೳ
     

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188. ·ͱΊ
     • KotlinͷSmart Castsͱܕਪ࿦Ͱɺ৑௕ͳίʔυΛݮΒ͠ɺҰ
     ෦μοΫλΠϐϯάͷΑ͏ͳॻ͖৺஍ΛಘΔ͜ͱ͕Մೳʂ
     
     • ॊೈͳδΣωϦΫεAPIΛ࢖͏͜ͱͰɺॊೈͳAPI͕ߏஙग़དྷ
     Δʂ
     
     • NothingܕΛ࢖͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ
     
     • Sealed classΛ࢖͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ
     

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189. Kotlin Fest
     2019
     ࠤ౻ ൏ / Sato Shun
     
     Twitter: @stsn_jp
     
     GitHub: satoshun
     Kotlinܕ࣮ફೖ໳
     

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