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

1. Kotlin Fest 2019 ࠤ౻ ൏ / Sato Shun Twitter: @stsn_jp GitHub: satoshun Kotlinܕ࣮ફೖ໳
2. ֓ཁ • KotlinͰ͸Javaʹ͸ͳ͍༷ʑͳܕʹؔ͢Δػೳ͕௥Ճ͞Εͨ ͷͰɺͦΕΒͷղઆ • ॳֶऀ޲͚ͷ಺༰ʹͳ͓ͬͯΓ·͢
3. ໨࣍ • Smart Casts • AnyɺUnitɺNothing • δΣωϦΫε • Sealed class • ؔ਺ܕ
4. •Smart Casts • AnyɺUnitɺNothing • δΣωϦΫε • Sealed class • ؔ਺ܕ
5. Smart Casts • ifࣜɺwhenࣜɺisɺasͳͲͷ࣮ߦޙʹɺ໌ࣔతʹܕΩϟετ ͠ͳͯ͘΋ɺܕΛਪ࿦ͯ͘͠ΕΔ • flow-sensitive typing (flow typing)ͱݺ͹ΕΔܕγεςϜ
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
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
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
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
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
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
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
13. if (hoge() && obj is Int) { a obj.toLong() } a if (obj is String && obj is Int) { a obj.length obj.toLong() } a
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
15. class Hoge { a private var obj: Any = "a" fun test() { a if (obj is String) { a print(obj.length) } a } a } a
16. class Hoge { a private var obj: Any = "a" fun test() { a if (obj is String) { a print(obj.length) } a } a } a ❌
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
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
19. val strs: List<String>? = … a if (!strs.isNullOrEmpty()) { a println(strs!!.size) } a
20. val strs: List<String>? = … a if (!strs.isNullOrEmpty()) { a println(strs.size) } a
21. Contracts • Smart CastsΛ֦ு͢Δػೳ • ؔ਺ݺͼग़͠ͷ݁ՌΛ΋ͱʹɺSmart Casts͢Δ͜ͱ͕ग़དྷ Δ
22. public inline fun <T> Collection<T>?.isNullOrEmpty(): Boolean { a contract { a returns(false) implies (this@isNullOrEmpty != null) } a return this == null || this.isEmpty() } a
23. public inline fun <T> Collection<T>?.isNullOrEmpty(): Boolean { a contract { a returns(false) implies (this@isNullOrEmpty != null) } a return this == null || this.isEmpty() } a
24. public inline fun <T> Collection<T>?.isNullOrEmpty(): Boolean { a contract { a returns(false) implies (this@isNullOrEmpty != null) } a return this == null || this.isEmpty() } a
25. public inline fun <T> Collection<T>?.isNullOrEmpty(): Boolean { a contract { a returns(false) implies (this@isNullOrEmpty != null) } a return this == null || this.isEmpty() } a
26. val strs: List<String>? = … a if (!strs.isNullOrEmpty()) { a println(strs!!.size) } a
27. val strs: List<String>? = … a if (!strs.isNullOrEmpty()) { a println(strs.size) } a
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
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
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)
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)
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)
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)
34. public inline fun <R> run(block: () -> R): R { a contract { a callsInPlace(block, InvocationKind.EXACTLY_ONCE) } a return block() } a
35. public inline fun <R> run(block: () -> R): R { a contract { a callsInPlace(block, InvocationKind.EXACTLY_ONCE) } a return block() } a
36. public inline fun <R> 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
37. public inline fun <R> 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
38. fun checkObj(obj: Any?): Boolean { a return obj != null } a if (checkObj(obj)) { a obj!!.javaClass } a
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
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
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
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
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
44. • Smart Casts •AnyɺUnitɺNothing • δΣωϦΫε • Sealed class • ؔ਺ܕ
45. Anyܕ • ͢΂ͯͷKotlinͷΫϥεͷεʔύʔΫϥε • ϧʔτΫϥε • Javaͷ৔߹ɺjava.lang.Object͕ϧʔτΫϥε
46. Anyܕ • JavaͷObjectͱҧ͏఺͸Ͳ͔͜ʁ • waitɺnotifyϝιου͕࢖͑ͳ͍ • ໌ࣔతʹjava.lang.ObjectܕʹΩϟετ͢Ε͹ݺͼग़ͤΔ • getClassϝιου͕֦ுؔ਺ʹ • public inline val <T : Any> T.javaClass: Class<T> • cloneɺfinalizeϝιου
47. val s = "" s.notify()
48. val s = "" (s as Object).notify()
49. Unitܕ • JavaͰ͍͏ͱ͜ΖͷvoidΛදݱ͢ΔΫϥε • ฦΓ஋͕ۭͰ͋Δ͜ͱΛද͢
50. fun empty() { a } a empty()
51. fun empty(): Unit { a } a empty()
52. fun empty(): Unit { a } a val e = empty() println(e)
53. fun empty() { a } a val e = empty() println(e)
54. Nothingܕ • ͢΂ͯͷKotlinͷΫϥεͷαϒΫϥε • ஋͕ଘࡏ͠ͳ͍͜ͱΛࣔ͢ • ਖ਼ৗऴྃ͢Δ͜ͱ͕ͳ͍ؔ਺ͷฦΓ஋ʹ࢖͑Δ
55. fun getName(): String { a return "name" } a fun fail() { a throw RuntimeException() } a
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
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
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
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)
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)
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)
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)
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)
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)
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)
66. fun test(any: Any): String { a when (any) { a is Int -> return "int" else -> fail() } a return "error" } a
67. fun test(any: Any): String { a when (any) { a is Int -> return "int" else -> fail() } a return "error" } a NothingܕͳͷͰɺ͜ͷݺͼग़͠͸ਖ਼ৗʹऴྃ͠ͳ͍ ͜ͷelse͸ඞࣦͣഊ͢Δ
68. fun test(any: Any): String { a when (any) { a is Int -> return "int" else -> fail() } a } a
69. // ඪ४ؔ਺ public inline fun TODO(): Nothing = throw NotImplementedError() // KotlinTest fun fail(msg: String): Nothing = throw Failures.failure(msg)
70. // Kotlin/kotlinx.collections.immutable internal companion object { internal val EMPTY = TrieNode<Nothing>(0, emptyArray()) } // airbnb/MvRx object Uninitialized : Async<Nothing>(complete = false, shouldLoad = true), Incomplete
71. fun test2() { a while (true) { a println(".") } a } a
72. fun test2(): Nothing { a while (true) { a println(".") } a } a
73. Nothing?ܕ • Nothing?ܕ΋ଘࡏ͢Δ • Nothing͸஋ͱͯ͠ଘࡏ͠ͳ͍ͷͰɺnullͷΈΛڐՄ͢Δ
74. // kotlintest/kotlintest interface Show<in A> { a fun supports(a: Any?): Boolean fun show(a: A): String } a object NullShow : Show<Nothing?> { a override fun supports(a: Any?): Boolean = a == null override fun show(a: Nothing?): String = "<null>" } a
75. • Smart Casts • AnyɺUnitɺNothing •δΣωϦΫε • Sealed class • ؔ਺ܕ
76. δΣωϦΫε • ෼ࢄΞϊςʔγϣϯʢvariance annotationʣ • outɺinम০ࢠ • એݴଆมੑ: declaration-site variance • where • reified • ֦ுؔ਺ + δΣωϦΫε
77. ෼ࢄΞϊςʔγϣϯ • out - ڞม: covariance • in - ൓ม: contravariance • ࢦఆͳ͠: ෆม: invariance
78. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ
79. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ
80. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ
81. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ • A<Number> -|> A<Int>ͷ৔߹ɺA͸൓มͰ͋Δ
82. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ • A<Number> -|> A<Int>ͷ৔߹ɺA͸൓มͰ͋Δ
83. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ • A<Number> -|> A<Int>ͷ৔߹ɺA͸൓มͰ͋Δ • A<Number>ɺ A<Int>͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ
84. ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A<Number> <|- A<Int>ͷ৔߹ɺA͸ڞมͰ͋Δ • A<Number> -|> A<Int>ͷ৔߹ɺA͸൓มͰ͋Δ • A<Number>ɺ A<Int>͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ
85. // ڞม val a: A<Int> = A<Int>() a val b: A<Number> = a
86. // ڞม val a: A<Int> = A<Int>() a val b: A<Number> = a // ൓ม val a: A<Number> = A<Number>() a val b: A<Int> = a
87. // ڞม val a: A<Int> = A<Int>() a val b: A<Number> = a // ൓ม val a: A<Number> = A<Number>() a val b: A<Int> = a // ෆม val a: A<Int> = A<Int>() a
88. interface Mapper<T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a
89. interface Mapper<T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a
90. interface Mapper<T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper)
91. interface Mapper<T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper) ❌
92. interface Mapper<T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper) ❌
93. interface Mapper<out T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper) ❌
94. interface Mapper<out T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper) ❌
95. interface Mapper<out T> { a fun map(s: String): T } a class IntMapper : Mapper<Int> { a override fun map(s: String): Int = s.toInt() } a fun hoge(mapper: Mapper<Number>) { a mapper.map("10") } a val mapper = IntMapper() hoge(mapper)
96. ListͱMutableList public interface List<out E> : Collection<E> public interface MutableList<E> : List<E>, …
97. ListͱMutableList public interface List<out E> : Collection<E> public interface MutableList<E> : List<E>, … • List͸outम০ࢠ͕෇͍͍ͯΔͷͰɺڞม • MutableList͸Կ΋෇͍͍ͯͳ͍ͷͰɺෆม
98. val strs: List<String> = listOf("a", “b")
99. val strs: List<String> = listOf("a", “b") val anys: List<Any> = strs
100. val strs: List<String> = listOf("a", “b") val anys: List<Any> = strs val a: Any = anys[0]
101. val strs: List<String> = listOf("a", “b") val anys: List<Any> = strs val a: Any = anys[0] val a2: Any? = anys2.getOrNull(1)
102. val strs: List<String> = listOf("a", “b") val anys: List<Any> = strs val a: Any = anys[0] val a2: Any? = anys2.getOrNull(1)
103. val strs: MutableList<String> = mutableListOf("a", "b")
104. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs
105. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs anys.add(10)
106. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs anys.add(10)
107. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs anys.add(10) val str: String = strs.last()
108. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs anys.add(10) val str: String = strs.last() ❌
109. val strs: MutableList<String> = mutableListOf("a", "b") val anys: MutableList<Any> = strs anys.add(10) val str: String = strs.last()
110. PECS • Producer Extends Consumer Super • Producer͸readͷੑ࣭Λ࣋ͭ • Consumer͸writeͷੑ࣭Λ࣋ͭ • List͸Producerͷੑ࣭ͷΈΛ࣋ͭͷͰɺExtends = out ڞมʹ ग़དྷΔ • MutableList͸ProducerͱConsumerͷੑ࣭Λ࣋ͭͷͰɺෆม
111. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺ • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ ͍
112. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺ • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ ͍ • fun <T : CharSequence> hoge(t: T) {…}
113. 2ͭҎ্ͷ্քΛ࣋ͭܕม਺ • 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖͸ɺׅހ಺ʹॻ͚͹ྑ ͍ • fun <T : CharSequence> hoge(t: T) {…} • 2ͭҎ্ͷ্քΛ࣋ͭ৔߹͸Ͳ͏͢Ε͹Α͍͔ʁ • ྫ͑͹ɺActivity͔ͭOnClickListenerΛ࣋ͭܕΛड͚ೖΕΔܕ ม਺Λఆ͍ٛͨ͠
114. class OnClickActivity() : Activity(), OnClickListener
115. class OnClickActivity() : Activity(), OnClickListener fun setClick(activity: OnClickActivity) { a } a
116. class OnClickActivity() : Activity(), OnClickListener fun setClick(activity: OnClickActivity) { a } a val activity = OnClickActivity() setClick(activity)
117. class OnClickActivity() : Activity(), OnClickListener fun setClick(activity: OnClickActivity) { a } a val activity = OnClickActivity() setClick(activity) class OnClickActivity2() : Activity(), OnClickListener
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)
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) ❌
120. fun setClick(activity: OnClickActivity) { a } a
121. fun <T> setClick(activity: T)
122. fun <T> setClick(activity: T) where T : Activity, T : OnClickListener { a } a
123. fun <T> setClick(activity: T) where T : Activity, T : OnClickListener { a } a val activity = OnClickActivity() setClick(activity)
124. fun <T> setClick(activity: T) where T : Activity, T : OnClickListener { } val activity = OnClickActivity() setClick(activity) val activity2 = OnClickActivity2() setClick(activity2)
125. internal abstract class NIOSocketImpl<out S>( override val channel: S, val selector: SelectorManager, val pool: ObjectPool<ByteBuffer>? ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope where S : java.nio.channels.ByteChannel, S : java.nio.channels.SelectableChannel Ktor
126. internal abstract class NIOSocketImpl<out S>( override val channel: S, val selector: SelectorManager, val pool: ObjectPool<ByteBuffer>? ) : ReadWriteSocket, SelectableBase(channel), CoroutineScope where S : java.nio.channels.ByteChannel, S : java.nio.channels.SelectableChannel Ktor
127. internal abstract class NIOSocketImpl<out S>( override val channel: S, val selector: SelectorManager, val pool: ObjectPool<ByteBuffer>? ) : 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<DatagramChannel>(channel, selector, DefaultDatagramByteBufferPool) Ktor
128. internal abstract class NIOSocketImpl<out S>( override val channel: S, val selector: SelectorManager, val pool: ObjectPool<ByteBuffer>? ) : 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<DatagramChannel>(channel, selector, DefaultDatagramByteBufferPool) internal class SocketImpl<out S : SocketChannel>( override val channel: S, private val socket: java.net.Socket, selector: SelectorManager ) : NIOSocketImpl<S>(channel, selector, pool = null), Socket Ktor
129. reified • ؔ਺಺͔Βܕม਺ʹΞΫηεग़དྷΔ • JavaͰ͸ܕม਺ʹϥϯλΠϜ࣌ʹΞΫηεͰ͖ͳ͍ • Type Erasureͱݺ͹ΕΔݴޠ࢓༷ͷͨΊɺίϯύΠϧޙʹܕม਺͕ ࡟আ͞ΕΔͨΊ
130. inline fun <reified T> hoge(obj: Any) { a println(T::class.java) a if (obj is T) { a println("obj is T") a } a } a
131. inline fun <reified T> hoge(obj: Any) { a println(T::class.java) a if (obj is T) { a println("obj is T") a } a } a
132. inline fun <reified T> hoge(obj: Any) { a println(T::class.java) a if (obj is T) { a println("obj is T") a } a } a
133. ֦ுؔ਺ + δΣωϦΫε • Kotlinͷ֦ுؔ਺ͱδΣωϦΫεΛ૊Έ߹ΘͤΔͱΑΓॊೈʹ ܕม਺Λίϯτϩʔϧ͢Δ͜ͱ͕ग़དྷΔ
134. class A<T>(val value: T) { a fun isNull(): Boolean { a return value != null } a } a
135. class A<T>(val value: T) { a fun isNull(): Boolean { a return value != null } a } a val a1: A<Int?> = A(null) a a1.isNull() a
136. class A<T>(val value: T) { a fun isNull(): Boolean { a return value != null } a } a val a1: A<Int?> = A(null) a a1.isNull() a val a2: A<Int> = A(10) a a2.isNull() a
137. class A<T>(val value: T) a fun <T : Any> A<T?>.isNull(): Boolean { a return value != null a } a val a1: A<Int?> = A(null) a a1.isNull() a val a2: A<Int> = A(10) a a2.isNull() a
138. class A<T>(val value: T) a fun <T : Any> A<T?>.isNull(): Boolean { a return value != null a } a val a1: A<Int?> = A(null) a a1.isNull() a val a2: A<Int> = A(10) a a2.isNull() a
139. class A<T>(val value: T) a fun <T : Any> A<T?>.isNull(): Boolean { a return value != null a } a val a1: A<Int?> = A(null) a a1.isNull() a val a2: A<Int> = A(10) a a2.isNull() a
140. class A<T>(val value: T) a fun <T : Any> A<T?>.isNull(): Boolean { a return value != null a } a val a1: A<Int?> = A(null) a a1.isNull() a val a2: A<Int> = A(10) a a2.isNull() a ❌
141. • Smart Casts • AnyɺUnitɺNothing • δΣωϦΫε •Sealed class • ؔ਺ܕ
142. Sealed class • ੍ݶ͞ΕͨαϒΫϥε֊૚ߏ଄Λ࡞Δ͜ͱ͕ग़དྷΔ • ಛघͳ༻్ͷabstract class
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
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
145. sealed class Either object Left : Either() object Right : Either() when (obj) { a Left -> println("is Left") Right -> println("is Right") } a
146. sealed͸classͰͷΈ༗ޮ • interfaceͩͱɺ༰қʹܧঝग़དྷͯ͠·͏ͨΊɺ੍໿ΛഁΕͯ ͠·͏
147. public abstract class Either { private Either() { } // $FF: synthetic method public Either(DefaultConstructorMarker $constructor_marker) { this(); } }
148. public abstract class Either { private Either() { } // $FF: synthetic method public Either(DefaultConstructorMarker $constructor_marker) { this(); } }
149. • Smart Casts • AnyɺUnitɺNothing • δΣωϦΫε • Sealed class •ؔ਺ܕ
150. ؔ਺ܕ • KotlinͰ͸ؔ਺ʢFunctionʣ͕ϑΝʔετΫϥεΦϒδΣΫτ • ม਺ɺؔ਺ͷҾ਺ɺ໭Γ஋ͳͲʹؔ਺ܕΛ࢖͏͜ͱ͕ग़དྷΔ
151. ؔ਺ܕ • Function0 ~ Function22ͷ22Ҿ਺·Ͱͷؔ਺ΠϯλʔϑΣʔε ͱɺͦΕҎ্ͷҾ਺༻ͷɺFunctionNΠϯλʔϑΣʔε͕ఆٛ ͞Ε͍ͯΔ • ্هͷؔ਺ΠϯλʔϑΣʔεʹίϯύΠϧ࣌ʹม׵͞ΕΔ
152. fun hoge(body: Function1<Int, String>) { a body(10) } a
153. fun hoge(body: (Int) -> String) { a body(10) } a
154. fun hoge(body: (Int) -> String) { a body(10) } a hoge { it.toString() } a
155. fun add(a1: Int, a2: Int): Int { a return a1 + a2 } a add add(10, 20)
156. fun add(a1: Int, a2: Int): Int { a return a1 + a2 } a add add(10, 20) val a: (Int, Int) -> Int = ::add
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)
158. } a add add(10, 20) val a: (Int, Int) -> Int = ::add a(10, 20) fun <P1, P2, R> ((P1, P2) -> R).curried(): (P1) -> (P2) -> R = { p1: P1 -> { p2: P2 -> this(p1, p2) } } a
159. } a add add(10, 20) val a: (Int, Int) -> Int = ::add a(10, 20) fun <P1, P2, R> ((P1, P2) -> R).curried(): (P1) -> (P2) -> R = { p1: P1 -> { p2: P2 -> this(p1, p2) } } a
160. } a add add(10, 20) val a: (Int, Int) -> Int = ::add a(10, 20) fun <P1, P2, R> ((P1, P2) -> R).curried(): (P1) -> (P2) -> R = { p1: P1 -> { p2: P2 -> this(p1, p2) } } a
161. } a add add(10, 20) val a: (Int, Int) -> Int = ::add a(10, 20) fun <P1, P2, R> ((P1, P2) -> R).curried(): (P1) -> (P2) -> R = { p1: P1 -> { p2: P2 -> this(p1, p2) } } a val curried = a.curried()
162. } a add add(10, 20) val a: (Int, Int) -> Int = ::add a(10, 20) fun <P1, P2, R> ((P1, P2) -> R).curried(): (P1) -> (P2) -> R = { p1: P1 -> { p2: P2 -> this(p1, p2) } } a val curried = a.curried() curried(10)(20)
163. class A : (Int) -> Unit { a override fun invoke(p1: Int) { a println("call $p1") } a } a val a = A() a.invoke(10)
164. class A : (Int) -> Unit { a override fun invoke(p1: Int) { a println("call $p1") } a } a val a = A() a(10)
165. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a
166. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a val a: (Number) -> Number = { it } a
167. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a val a: (Number) -> Number = { it } a val a1: (Int) -> Number = a
168. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a val a: (Number) -> Number = { it } a val a1: (Int) -> Number = a
169. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a val a: (Number) -> Number = { it } a val a1: (Int) -> Number = a val a2: (Number) -> Any = a
170. public interface Function1<in P1, out R> : Function<R> { public operator fun invoke(p1: P1): R } a val a: (Number) -> Number = { it } as val a1: (Int) -> Number = a val a2: (Number) -> Any = a
171. SAMม׵ • SAM? • Single Abstract Method • 1ͭͷந৅ϝιουΛ࣋ͭ • Kotlin͔ΒJavaఆٛͷSAMΛ࢖͏ͱ͖ʹɺϥϜμࣜͰ؆ܿʹ ॻ͘͜ͱ͕ग़དྷΔ
172. public class SamTest { a public static void foo(Runnable a, Runnable b) { a } a } a fun test() { a SamTest.foo({}) { a } a } a
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(); }
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
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 ❌
176. KotlinͷSAMม׵ͷ՝୊ • ෳ਺ͷSAMΛҾ਺ʹऔΔ৔߹ɺ1ͭͰ΋࣮ମΛ࢖ͬͯ͠·͏ ͱɺҙਤͨ͠ม׵͕ߦΘΕͳ͍
177. // RxJava val o1 = Observable.just(1) val o2 = Observable.just(2) val combination = Observable .combineLatest(o1, o2, { n1, n2 -> n1 to n2 }) a
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 <T1, T2, R> Observable<R> combineLatest( ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, BiFunction<? super T1, ? super T2, ? extends R> combiner ) a
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 <T1, T2, R> Observable<R> combineLatest( ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, BiFunction<? super T1, ? super T2, ? extends R> combiner ) a public interface ObservableSource<T> { a void subscribe(@NonNull Observer<? super T> observer); } ˇ
180. // RxJava val o1 = Observable.just(1) val o2 = Observable.just(2) val combination = Observable .combineLatest(o1, o2, { n1, n2 -> n1 to n2 })
181. // RxJava val o1 = Observable.just(1) val o2 = Observable.just(2) val combination = Observable .combineLatest(o1, o2, { n1, n2 -> n1 to n2 }) ❌
182. // RxJava val o1 = Observable.just(1) val o2 = Observable.just(2) val combination = Observable .combineLatest(o1, o2, BiFunction { n1, n2 -> n1 to n2 })
183. public static <T1, T2, R> Observable<R> combineLatest( ObservableSource<? extends T1> source1, ObservableSource<? extends T2> source2, BiFunction<? super T1, ? super T2, ? extends R> combiner ) a
184. public static <T1, T2, R> Observable<R> combineLatest( Observable<? extends T1> source1, Observable<? extends T2> source2, BiFunction<? super T1, ? super T2, ? extends R> combiner ) a
185. public static <T1, T2, R> Observable<R> 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 })
186. public static <T1, T2, R> Observable<R> 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 })
187. NewInference • kotlinͰ͸SAMม׵ͷ໰୊ʹରͯ͠ɺ৽͍͠ܕਪ࿦Λ։ൃͯ͠ ͍Δ • ݱࡏɺexperimentalͷཱͪҐஔ͕ͩɺઃఆͰenableʹ͢Δ͜ͱ ͕Մೳ
188. ·ͱΊ • KotlinͷSmart Castsͱܕਪ࿦Ͱɺ৑௕ͳίʔυΛݮΒ͠ɺҰ ෦μοΫλΠϐϯάͷΑ͏ͳॻ͖৺஍ΛಘΔ͜ͱ͕Մೳʂ • ॊೈͳδΣωϦΫεAPIΛ࢖͏͜ͱͰɺॊೈͳAPI͕ߏஙग़དྷ Δʂ • NothingܕΛ࢖͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ • Sealed classΛ࢖͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ
189. Kotlin Fest 2019 ࠤ౻ ൏ / Sato Shun Twitter: @stsn_jp GitHub: satoshun Kotlinܕ࣮ફೖ໳