Kotlinらしいコード #jkug

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KotlinΒ͍͠ίʔυ ୈճ͔Θ͍͍,PUMJOษڧձ ! ೔ຊ,PUMJOϢʔβάϧʔϓ  ௕ᖒଠ࿠!OHTX@UBSP

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ࣗݾ঺հ w ௕ᖒଠ࿠!OHTX@UBSP w ࢓ࣄͰ͸+BWB 4DBMB "OESPJE w ࣗশ,PUMJOΤϰΝϯδΣϦετ w ࡀɺֈ࠲ɺͱ͕େ޷͖

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Έͳ͞Μ KotlinΒ͍͠ίʔυ ॻ͍ͯ·͔͢ʁ

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w +BWBܦݧ͋Γˠ,PUMJO؆୯ ! w ؔ਺Ϧςϥϧɺߴ֊ؔ਺ w ֦ுؔ਺ɺ%FMFHBUFE1SPQFSUZ w /6--҆શ KotlinͬΆ͍ίʔυʁ ػೳଟͯ͘ ࢖͍͜ͳͤΜ ͱ͸ݴͬͯ΋ʜ

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ຊ೔ͷςʔϚ KotlinΒ͍͠ίʔυ KotlinͷػೳΛ׆͔ͨ͠ίʔυ

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୊ࡐ1. sum

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fun sum(xs: List): Int {! var sum = 0! for(x in ints) {! sum += x! }! return sum! }

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fun sum(xs: List): Int {! var sum = 0! for(x in ints) {! sum += x! }! return sum! } WBSݏͩͳʔ

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! }

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ຤ඌݺͼग़͠࠷దԽΛ༗ޮ

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ϩʔΧϧؔ਺

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } JGͰ΋FMTFͰ΋SFUVSO ؾ࣋ͪѱ͍ʜ JGͰ΋FMTFͰ΋SFUVSO ؾ࣋ͪѱ͍ʜ

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! }

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } JGFMTF͸ࣜ

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ΋ͬͱ ͔ͬ͜Α͘Ͱ͖Δ

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int =! if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! ! return go(xs, 0)! }

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fun sum(xs: List): Int {! @tailRecursive! fun go(xs: List, a: Int): Int =! if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! ! return go(xs, 0)! } ୯Ұࣜؔ਺

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fun sum(xs: List): Int =! xs.fold(0) { a, x -> a + x }

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fun sum(xs: List): Int =! xs.fold(0) { a, x -> a + x } ඪ४"1* ࠨ৞ΈࠐΈ

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fun sum(xs: List): Int =! xs.fold(0) { a, x -> a + x } ؔ਺Ϧςϥϧ

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fun List.sum(): Int =! fold(0) { a, x -> a + x }

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fun List.sum(): Int =! fold(0) { a, x -> a + x } ֦ுؔ਺

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No content

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(sumͳΜ͔ࣗ࡞͠ͳ͍)

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! ! ඪ४API fun Iterable.sum(): Int (sumͳΜ͔ࣗ࡞͠ͳ͍)

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୊ࡐ1. sum ·ͱΊ w WBSݏͩ w UBJM3FDVSTJWFͰ5$0 w ϩʔΧϧؔ਺ w JGFMTF͸ࣜ w GVOIPHF Ͱ୯Ұࣜؔ਺ w ֦ுؔ਺ w ඪ४"1*Λ࢖͏

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୊ࡐ2. nullable

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// ໊લΛऔಘͰ͖Δ! fun getName(): String?! ! // อଘͰ͖Δ! fun save(s: String): Unit

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val name: String? = getName()! if(name != null) {! save(name)! }

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val name: String? = getName()! if(name != null) {! save(name)! } OVMMνΣοΫ ͜ͷதͰOBNF͸ OPU/VMMͱͯ͠ѻ͑Δ

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name?.let {! name -> save(name)! }

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name?.let {! name -> save(name)! } ඪ४"1* MFUؔ਺

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name?.let {! name -> save(name)! } ඪ४"1* MFUؔ਺ ҆શݺͼग़͠

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name?.let {! save(it)! }

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name?.let {! save(it)! } ҉໧ͷม਺ JU

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name?.let(::save)

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name?.let(::save) ؔ਺ࢀর

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୊ࡐ2. nullable ·ͱΊ w OVMMνΣοΫ͍͢͝ w ͷ҆શݺͼग़͠ศར w MFUؔ਺໘ന͍ w ҉໧ͷม਺JU w ؔ਺ࢀর w ͓·͚IUUQTTQFBLFSEFDLDPNOUBSP LPUMJOOVNCFSTIJCVJHVKWN

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୊ࡐ3. immutable

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class User(id: Long, name: String) {! val id = id! val name = name! ! class Builder {! var id: Long? = null! var name: String? = null! ! fun id(id: Long): Builder {! this.id = id! return this! }! ! fun name(name: String): Builder {! this.name = name! return this! }! ! fun build(): User {! val id = checkNotNull(id)! val name = checkNotNull(name)! return User(id, name)! }!

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val taro = User.Builder()! .id(123)! .name(“Taro”)! ! .build()! ! val jiro = taro.builder()! .name(“Jiro”)! .build() qVFOUJOUFSGBDFͰ JNNVUBCMFͳ΍ͭ

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data class User(! val id: Long,! val name: String! )

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data class User(! val id: Long,! val name: String! ) EBUBΞϊςʔγϣϯ ϓϩύςΟ

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val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”)

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val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”) ໊લ෇͖Ҿ਺

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val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”) EBUBΞϊςʔγϣϯʹΑΔ DPQZϝιου

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୊ࡐ3. immutable ·ͱΊ w EBUBΞϊςʔγϣϯڧ͍ w ໊લ෇͖Ҿ਺ w ˢ΋͏-PNCPLܥ#VJMEFSύλʔϯཁΒͳ͍

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୊ࡐ4. decorator

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class GreetableCharSeq! (private val cs: CharSequence): CharSequence {! ! fun hello() {! println("Hello, ${cs}")! }! ! override fun length(): Int = cs.length()! override fun charAt(index: Int): Char = cs.charAt(index)! override fun subSequence(start: Int, end: Int): CharSequence =! cs.subSequence(start, end)! }

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class GreetableCharSeq! (private val cs: CharSequence): CharSequence by cs {! fun hello() {! println("Hello, ${cs}")! }! }

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class GreetableCharSeq! (private val cs: CharSequence): CharSequence by cs {! fun hello() {! println("Hello, ${cs}")! }! } CZͰҕৡ ҕৡ͢Δ͚ͩͷ ϝιου͸هड़ෆཁ

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࣮ࡍ͸… fun CharSequence.hello() {! println(“Hello, $this”)! }

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୊ࡐ4. decorator ·ͱΊ w EFDPSBUPSύλʔϯΈ͍ͨͳͷ͍ͨ͠ͱ͖͸ CZΩʔϫʔυʹΑΔҕৡͷ࢓૊ΈΛ࢖͏ w ࠓճͷྫͰ͸֦ுؔ਺ͰࡁΜͩ

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͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠