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Kotlin Fest
2019
ࠤ౻ ൏ / Sato Shun
Twitter: @stsn_jp
GitHub: satoshun
Kotlinܕ࣮ફೖ
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֓ཁ
• KotlinͰJavaʹͳ͍༷ʑͳܕʹؔ͢Δػೳ͕Ճ͞Εͨ
ͷͰɺͦΕΒͷղઆ
• ॳֶऀ͚ͷ༰ʹͳ͓ͬͯΓ·͢
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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
͠ͳͯ͘ɺܕΛਪͯ͘͠ΕΔ
• flow-sensitive typing (flow typing)ͱݺΕΔܕγεςϜ
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Smart Casts
• ifࣜɺwhenࣜɺisɺasͳͲͷ࣮ߦޙʹɺ໌ࣔతʹܕΩϟετ
͠ͳͯ͘ɺܕΛਪͯ͘͠ΕΔ
• flow-sensitive typing (flow typing)ͱݺΕΔܕγεςϜ
• ͳܕΩϟετΛܰݮ͢Δ
• ಈతܕ͚ݴޠͷμοΫλΠϐϯάͷΑ͏ͳॻ͖৺
• 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
• ؔݺͼग़͠ͷ݁ՌΛͱʹɺSmart 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
• JavaͷObjectͱҧ͏Ͳ͔͜ʁ
• waitɺnotifyϝιου͕͑ͳ͍
• ໌ࣔతʹjava.lang.ObjectܕʹΩϟετ͢Εݺͼग़ͤΔ
• getClassϝιου͕֦ுؔʹ
• 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
• ฦΓ͕ۭͰ͋Δ͜ͱΛද͢
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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
• ਖ਼ৗऴྃ͢Δ͜ͱ͕ͳ͍ؔͷฦΓʹ͑Δ
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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
NothingܕͳͷͰɺ͜ͷݺͼग़͠ਖ਼ৗʹऴྃ͠ͳ͍
͜ͷelseඞࣦͣഊ͢Δ
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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?ܕଘࡏ͢Δ
• Nothingͱͯ͠ଘࡏ͠ͳ͍ͷͰɺnullͷΈΛڐՄ͢Δ
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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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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
• A -|> Aͷ߹ɺAมͰ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
• A -|> Aͷ߹ɺAมͰ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
• A -|> Aͷ߹ɺAมͰ͋Δ
• Aɺ A͕ؔͳ͍߹ɺAෆมͰ͋Δ
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ڞมɺมɺෆม
• Number <|- Intͷܧঝ͕ؔ͋Δ
• A <|- Aͷ߹ɺAڞมͰ͋Δ
• A -|> Aͷ߹ɺAมͰ͋Δ
• Aɺ A͕ؔͳ͍߹ɺAෆมͰ͋Δ
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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, …
• Listoutम০ࢠ͕͍͍ͯΔͷͰɺڞม
• MutableListԿ͍͍ͯͳ͍ͷͰɺෆม
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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
• Producerreadͷੑ࣭Λ࣋ͭ
• Consumerwriteͷੑ࣭Λ࣋ͭ
• ListProducerͷੑ࣭ͷΈΛ࣋ͭͷͰɺExtends = out ڞมʹ
ग़དྷΔ
• MutableListProducerͱConsumerͷੑ࣭Λ࣋ͭͷͰɺෆม
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2ͭҎ্ͷ্քΛ࣋ͭܕม
• 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖ɺׅހʹॻ͚ྑ
͍
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2ͭҎ্ͷ্քΛ࣋ͭܕม
• 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖ɺׅހʹॻ͚ྑ
͍
• fun hoge(t: T) {…}
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2ͭҎ্ͷ্քΛ࣋ͭܕม
• 1ͭͷ্քʢupper boundʣΛ࣋ͭͱ͖ɺׅހʹॻ͚ྑ
͍
• fun hoge(t: T) {…}
• 2ͭҎ্ͷ্քΛ࣋ͭ߹Ͳ͏͢ΕΑ͍͔ʁ
• ྫ͑ɺActivity͔ͭOnClickListenerΛ࣋ͭܕΛड͚ೖΕΔܕ
มΛఆ͍ٛͨ͠
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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
• ͔ؔΒܕมʹΞΫηεग़དྷΔ
• JavaͰܕมʹϥϯλΠϜ࣌ʹΞΫηεͰ͖ͳ͍
• Type ErasureͱݺΕΔݴޠ༷ͷͨΊɺίϯύΠϧޙʹܕม͕
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
• Kotlinͷ֦ுؔͱδΣωϦΫεΛΈ߹ΘͤΔͱΑΓॊೈʹ
ܕมΛίϯτϩʔϧ͢Δ͜ͱ͕ग़དྷΔ
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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֊ߏΛ࡞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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sealedclassͰͷΈ༗ޮ
• interfaceͩͱɺ༰қʹܧঝग़དྷͯ͠·͏ͨΊɺ੍ΛഁΕͯ
͠·͏
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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
• KotlinͰؔʢFunctionʣ͕ϑΝʔετΫϥεΦϒδΣΫτ
• มɺؔͷҾɺΓͳͲʹؔܕΛ͏͜ͱ͕ग़དྷΔ
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ؔܕ
• Function0 ~ Function22ͷ22Ҿ·ͰͷؔΠϯλʔϑΣʔε
ͱɺͦΕҎ্ͷҾ༻ͷɺFunctionNΠϯλʔϑΣʔε͕ఆٛ
͞Ε͍ͯΔ
• ্هͷؔΠϯλʔϑΣʔεʹίϯύΠϧ࣌ʹม͞ΕΔ
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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
• 1ͭͷநϝιουΛ࣋ͭ
• Kotlin͔ΒJavaఆٛͷSAMΛ͏ͱ͖ʹɺϥϜμࣜͰ؆ܿ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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KotlinͷSAMมͷ՝
• ෳͷSAMΛҾʹऔΔ߹ɺ1ͭͰ࣮ମΛͬͯ͠·͏
ͱɺҙਤͨ͠ม͕ߦΘΕͳ͍
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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
• kotlinͰSAMมͷʹରͯ͠ɺ৽͍͠ܕਪΛ։ൃͯ͠
͍Δ
• ݱࡏɺexperimentalͷཱͪҐஔ͕ͩɺઃఆͰenableʹ͢Δ͜ͱ
͕Մೳ
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·ͱΊ
• KotlinͷSmart CastsͱܕਪͰɺͳίʔυΛݮΒ͠ɺҰ
෦μοΫλΠϐϯάͷΑ͏ͳॻ͖৺ΛಘΔ͜ͱ͕Մೳʂ
• ॊೈͳδΣωϦΫεAPIΛ͏͜ͱͰɺॊೈͳAPI͕ߏஙग़དྷ
Δʂ
• NothingܕΛ͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ
• Sealed classΛ͏͜ͱͰɺॊೈͳAPIΛߏஙͰ͖Δʂ
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Kotlin Fest
2019
ࠤ౻ ൏ / Sato Shun
Twitter: @stsn_jp
GitHub: satoshun
Kotlinܕ࣮ફೖ