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

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

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

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

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

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

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

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Contracts • Smart CastsΛ֦ு͢Δػೳ • ؔ਺ݺͼग़͠ͷ݁ՌΛ΋ͱʹɺSmart Casts͢Δ͜ͱ͕ग़དྷ Δ

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

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

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

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

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

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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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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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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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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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@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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• Smart Casts •AnyɺUnitɺNothing • δΣωϦΫε • Sealed class • ؔ਺ܕ

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

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

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val s = "" s.notify()

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

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Unitܕ • JavaͰ͍͏ͱ͜ΖͷvoidΛදݱ͢ΔΫϥε • ฦΓ஋͕ۭͰ͋Δ͜ͱΛද͢

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fun empty() { a } a empty()

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

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

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

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

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

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

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

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

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

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

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

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// 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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• Smart Casts • AnyɺUnitɺNothing •δΣωϦΫε • Sealed class • ؔ਺ܕ

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

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

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ • Aɺ A͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ

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ڞมɺ൓มɺෆม • Number <|- Intͷܧঝؔ܎͕͋Δ • A <|- Aͷ৔߹ɺA͸ڞมͰ͋Δ • A -|> Aͷ৔߹ɺA͸൓มͰ͋Δ • Aɺ A͕ؔ܎ͳ͍৔߹ɺA͸ෆมͰ͋Δ

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// ڞม val a: A = A() a val b: A = a

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

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// 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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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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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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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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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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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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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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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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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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ListͱMutableList public interface List : Collection public interface MutableList : List, …

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

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val strs: List = listOf("a", “b")

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

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

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

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

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

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

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

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

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

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

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

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

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

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class OnClickActivity() : Activity(), OnClickListener

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

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

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

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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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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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fun setClick(activity: OnClickActivity) { a } a

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fun setClick(activity: T)

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

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

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

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

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

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

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

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

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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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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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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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sealed͸classͰͷΈ༗ޮ • interfaceͩͱɺ༰қʹܧঝग़དྷͯ͠·͏ͨΊɺ੍໿ΛഁΕͯ ͠·͏

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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