ぼくらがScalaを選ぶ理由〜入門編〜

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΅͘Β͕ScalaΛબͿཧ༝ ʙೖ໳ฤʙ 2015-08-27 ୈ3ճSpeeeTechParty גࣜձࣾSpeee ੢Ԭ׮݉

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ࣗݾ঺հ • ੢Ԭ׮݉ʢʹ͓͔͠ ͻΖ͔ͣʣ • Speee ΠΤ΢ʔϧ ϦʔυΤϯδχΞ  αʔόαΠυεϖγϟϦετ • twitterɿ@nisshieeorg • ޷͖ͳݴޠɿScala • ΠΧIDɿnisshieeorg

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υϠΝɾɾɾ http://markezine.jp/article/detail/22902

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΅͘ͷϓϩάϥϛϯάݴޠྺ • ࠷ॳ͸ಠֶͰBasicͱ͔HSPͱ͔Javaͱ͔ • ࢓ࣄͰ͸JavaɺPHPϝΠϯʹ4೥΄Ͳ • ࠷ۙ͸Ruby + Scala • ScalaΛ࢝Ίͨͷ͸4೥લ͙Β͍ʢझຯͰʣ

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ͳͥScalaΛ࢝Ίͨͷ͔ • ͍͍ͩͨTwitterͷ͍ͤʢTL͕ͳ͝΍ͩͬͨʣ • ؔ਺ܕݴޠͷ࣌୅͕དྷͦ͏ͳงғؾ • ࣮͸࠷ॳ͸F#࢝Ίͨ • F#޷͖͚ͩͲ.NETͰಈ͍ͯ΋خ͘͠ͳ͔ͬͨ • JVMͰಈ͘ͷ͕͋ΔΒ͍͠ʂ → Scala

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ScalaͬͯͲΜͳݴޠʁ

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ScalaͬͯͲΜͳݴޠʁ • ੩తܕ෇͚ؔ਺ܕ + OOP • ʮ౷߹ʯͱ͍͏ࢥ૝ • JVM্Ͱಈ࡞ʢੲ͸.NET΋αϙʔτͯͨ͠ʣ • Martin Oderskyڭत࡞ʢ2004 public releaseʣ • εΠε࿈๜޻Պେֶڭत • খా޷ઌੜ Miles Sabin https://www.ﬂickr.com/photos/montpelier/3957416434/

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ScalaͬͯͲΜͳݴޠʁ • Typesafe Inc. • Oderskyڭत+Scala։ൃऀ (2011) • Scalaຊମ΍ϥΠϒϥϦͷ։ൃ + αϙʔτ • Twitter͕Rails͔ΒScalaʹҠߦ (2008) • ࠷ۙͰ͸ࠃ಺࠾༻ࣄྫ΋ • υϫϯΰɺChatworkɺ͸ͯͳɺCAɺetc and Speee

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ඇެࣜϚείοτ

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ScalaͩͱԿ͕خ͍͠ͷʁ

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ྫ͑͹͸ͯͳ͞Μ http://songmu.github.io/slides/yapc-asia2015/ YAPC::Asia Tokyo 2015ͷTalkΑΓ

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ؔ਺ʢ਺ֶͷ͓࿩ʣ ఆٛҬ ஋Ҭ ؔ਺ͷೖྗ஋ͱͯ͠औΓಘΔൣғɿఆٛҬ

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ؔ਺ʢϓϩάϥϛϯάͷ͓࿩ʣ Ҿ਺ ໭Γ஋

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ؔ਺ͷςετ Ҿ਺ ໭Γ஋ (1) ͍Ζ͍ΖͳҾ਺Λ  ೖΕͯΈΔ (2) ݁Ռ͕ૂ͍௨Γ͔  νΣοΫ

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Ͷɺ؆୯Ͱ͠ΐ

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ͪΐͬͱ଴ͬͨ

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͋ͳͨͷςετɺେৎ෉ʁ Ҿ਺ ໭Γ஋ ؔ਺ͷఆٛҬΛे෼ʹ໢ཏ͍ͯ͠·͔͢ʁ ͱ͍͏͔ͦ΋ͦ΋ɺ͋ͳͨࣗ਎  ఆٛҬΛͪΌΜͱ೺Ѳ͍ͯ͠·͔͢ʁ ʁ

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͋ͳͨͷςετɺେৎ෉ʁ Ҿ਺ ໭Γ஋ ؔ਺ͷ;Δ·͍ʹӨڹΛ༩͑Δೖྗ஋͸  Ҿ਺͚ͩͰ͔͢ʁ Πϯελϯεม਺ʁ ؀ڥม਺ʁ DBͷ஋ʁ ݱࡏ࣌ࠁʁ

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͋ͳͨͷςετɺେৎ෉ʁ Ҿ਺ ໭Γ஋ ؔ਺ͷ;Δ·͍ͷ݁Ռ͕ݱΕΔग़ྗ஋͸  ໭Γ஋͚ͩͰ͔͢ʁ Πϯελϯεม਺ʁ ը໘ʁ DBͷ஋ʁ ྫ֎ʁ

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େৎ෉ɺͪΌΜͱ  શ෦೺Ѳͯ͠ΔΑʂ

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　　　　　　　_,,;' '" '' ゛''" ゛' ';;,, 　　　　　　（rヽ,;''"""''゛゛゛'';, ﾉｒ）　　　　　　,;'゛ i ＿　　、＿ iヽ゛';,　　　　お前それ、1年後や、仕様変更後や　　　　　 ,;'" ''| ヽ・〉　〈・ノ |ﾞ゛ `';, 他人の書いたコードを保守するときでも　　　　　 ,;''　"|　　 ▼　　 |ﾞ゛　`';, 同じ事言えんの？　　　　　 ,;''　　ヽ＿人＿ /　　,;'_ 　　　　／ｼ、　ヽ⌒⌒ /　　ﾘ　＼　　　　|　　　"ｒ,,　｀"'''ﾞ´　　,,ﾐ゛　　 | 　　　　|　　　　ﾘ、　　　　,ﾘ　　　　| 　　　　|　　　i 　　゛ｒ、ﾉ,,ｒ"　i　　　_| 　　　　|　　　｀ー――----┴ ⌒´ ）　　　　（ヽ　＿＿＿＿＿＿ ,, ＿´）　　　　（_⌒ ＿＿＿＿＿＿ ,, ィ　　　　　　丁　　　　　　　　　　 | 　　　　　　 |　　　　　　　　　　　|

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͡Ό͋Ͳ͏͢Δ͔

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ఆٛҬΛ໌֬ʹ͢Δ • ͜Εͦ͜ܕͷ໾໨ × υΩϡϝϯτΛಡΊ͹શͯΘ͔Δ ̋ γάχνϟΛݟΕ͹શͯΘ͔Δ // Scala class List[A] { def count(p: A => Boolean): Int = ??? } ! # Ruby (͜Εɺطʹશ෦υΩϡϝϯτɻ࣮ࡍʹ͸ϝιου಺Ͱif෼ذ͍ͯ͠Δ) count -> Integer count(item) -> Integer count {|obj| ... } -> Integer

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sealed trait, case class • ࣗ࡞ͷܕ΋ఆٛҬΛ໌֬ʹ͢Δ sealed trait Item ! sealed trait Weapon extends Item case class Sword(power: Int) extends Weapon ! sealed trait Medicine extends Item case object Antidote extends Medicine ! // —————————————————————————— ! def buy(item: Item) def equip(weapon: Weapon) def take(medicine: Medicine)

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ʢ༨ஊʣ໢ཏੑνΣοΫ def buy(item: Item) = item match { case sword: Sword => ??? case Antidote => ??? } // —————————————————————————- ! def buy(item: Item) = item match { case sword: Sword => ??? } // ↑ ίϯύΠϧΤϥʔ :29: warning: match may not be exhaustive. It would fail on the following input: Antidote def buy(item: Item) = item match { ^ error: No warnings can be incurred under -Xfatal-warnings.

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ೖྗ஋ɺग़ྗ஋ͷൣғ Ҿ਺ ໭Γ஋ Πϯελϯεม਺ʁ ؀ڥม਺ʁ DBͷ஋ʁ ݱࡏ࣌ࠁʁ Πϯελϯεม਺ʁ ը໘ʁ DBͷ஋ʁ ྫ֎ʁ • ͍͍ͩͨ೺Ѳ͖͠Ε͍ͯͳͯ͘όάΔʢܦݧஊʣ • ʮ೺ѲͰ͖Δʯͱ͍͏ݬ૝͸ࣺͯͨ΄͏͕ྑ͍ 4DBMBʹݶΒͳ͍Ұൠతͳ࿩

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ೖྗ஋ɺग़ྗ஋Λݶఆ Ҿ਺ ໭Γ஋ Πϯελϯεม਺ʁ ؀ڥม਺ʁ DBͷ஋ʁ ݱࡏ࣌ࠁʁ Πϯελϯεม਺ʁ ը໘ʁ DBͷ஋ʁ ྫ֎ʁ • Ҿ਺͚ͩͰؔ਺ͷ;Δ·͍͕ܾ·Δʢࢀরಁ໌ੑʣ • ໭Γ஋Ҏ֎ͷӨڹʢ෭࡞༻ʣ͕ͳ͍

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ࢀরಁ໌Ͱ෭࡞༻ͷͳ͍ؔ਺ • ඞཁͳ৘ใ͸શͯҾ਺ʹ • ݁Ռ͸શͯ໭Γ஋ʹʢྫ֎Λ࢖Θͳ͍ʣ • ʮͱ͸ݴ͑ɺDBͷಡΈॻ͖͠ͳ͍Θ͚ʹ͸ʯ • ʮDBΞΫηεͷ͋Δؔ਺܈ʯΛ੾Γ཭͢ • IOϞφυͱ͔

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ScalaͳΒ • ͜͏͍͏ͷ͕΍Γ΍͍͢Αʂ

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implicit parameter ஫ʣ؀ڥ৘ใͷimplicit parameterԽ͸ࢍ൱͋Γ·͢ def hoge(args: Args, env: Env): Res = ??? def fuga(args: Args, env: Env): Res = hoge(args, env) ! fuga(args, env) // ؔ਺ίʔϧ࣌ʹຖճ؀ڥ৘ใΛҾ਺ʹ౉͢ͷ͸μϧ͍ ! // —————————————————————————————————— def hoge(args: Args)(implicit env: Env) = ??? def fuga(args: Args)(implicit env: Env) = hoge(args) ! implicit val env: Env = ??? fuga(args)

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Option • ஋͕͋Δʢ੒ޭͯ͠ɺ஋͕ฦΔʣ • ஋͕ͳ͍ʢࣦഊʣ sealed trait Option[A] case class Some[A](a: A) extends Option[A] case object None extends Option[Nothing] ! // ———————————————————————————- ! class List[A] { def find(p: A => Boolean): Option[A] = ??? }

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໭͞ΕͨOptionΛѻ͏ val found: Option[A] = aList.find(condition) ! // BAD (ݹ͖ྑ͖nullνΣοΫͱҰॹ) if (found.isDefined) { val a = found.get ??? } ! // So so ... (લड़ͷ໢ཏੑνΣοΫ΋૸Δ) found match { case Some(a) => ??? case None => ??? }

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Optionʹؔ਺Λ౉͢ // GOOD!! // aToB: A => B found.map(aToB) // => Option[B] ! // failableAToB: A => Option[B] found.flatMap(failableAToB) // => Option[B] ! for { a <- found b <- failableAToB(a) c <- failableBToC(b) d <- failableCToD(c) } yield dToE(d) // => Option[E]

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EitherͰʮࣦഊཧ༝ʯΛฦ͢ sealed trait Either[E, A] case class Right[A](a: A) extends Either[Nothing, A] case class Left[E](e: E) extends Either[E, Nothing] ! // ʮࣦഊʯͷఆٛ sealed trait EquipFailure case class JobMismatch(j: Job, w: Weapon) extends EquipFailure case class LevelShortage(l: Level, w: Weapon) extends EquipFailure ! // EitherΛฦ͢ def equip(weapon: Weapon): Either[EquipFailure, Status] = ???

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໭͞ΕͨEitherΛѻ͏ equip(weapon).fold({ case JobMismatch(j, w) => ??? case LevelShortage(l, w) => ??? }, { status => ??? })

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ཁ͢Δʹ Կ͕ݴ͍͔͔ͨͬͨ

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γάχνϟͰશͯ෼͔Δ • ໋໊Λ͕Μ͹Δ ← ඞཁ͕ͩɺݶք͕͋Δ • γάχνϟʹදΕͳ͍΋ͷ͸࢖Θͳ͍ • ʮܕͷ஌ࣝʯΛར༻͢Δʢʮܕ͸υΩϡϝϯτʯʣ • ܕͰ͔ͬͪΓݻΊΔ͜ͱ͸طଘݴޠͰ΋Ͱ͖͔ͨ΋ ͠Εͳ͍͕ɺѻ͍ͮΒ͔ͬͨ  → Ͱ΋ɺScalaͳΒָʹͰ͖ΔΑʂ ࠓ ೔ Ұ ൪ େ ࣄ ͳ   εϥ Π υ

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͕࣌ؒ͋Ε͹  Scalaͷ໘ന͍ػೳ঺հ

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String Interpolation • ଞͷݴޠͩͱʮม਺ల։ʯͱ͔ݴΘΕΔ΍ͭ ! ! • ʮsʯͷଞʹʮfʯ΋͋Δʢิؒࢠʣ val name: String = "Nishioka" val age: Int = 28 val s: String = s"${name}͘Μ${age}͍͞" // => Nishioka͘Μ28͍͞ val better: String = f"${name}%s͘Μ${age}%X͍͞" // => Nishioka͘Μ1C͍͞

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String Interpolation • ิؒࢠ͸ࣗ෼Ͱ࡞Δ͜ͱ΋Ͱ͖Δʂ • ྫɿScalikeJDBCʢhttp://scalikejdbc.org/ʣ object EmployeeRepository {  def findBy(dep: Department)(implicit ses: DBSession) = sql""" select * from employees where department_id = ${dep.id} """.map(extract).list.apply }

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lazy val • ஗ԆධՁʢ࠷ॳʹ࢖ΘΕͨͱ͖ʹॳظԽʣ scala> lazy val s: String = { | println("initialized") | "a string" | } s: String = ! scala> println(s) initialized a string ! scala> println(s) a string

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Future • ϊϯϒϩοΩϯάʂඇಉظʂ val f: Future[Result] = Future { longTimeFunc() } // ↑ ϊϯϒϩοΩϯά ! f onComplete { case Success(result) => ??? case Failure(thrown) => ??? } ! f onSuccess { case result => ??? } f onFailure { case thrown => ??? }

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Futureͷ߹੒ val fa: Future[A] = Future { ??? } ! // aToB: A => B fa.map(aToB) // => Future[B] ! // longTimeAToB: A => Future[B] fa.flatMap(longTimeAToB) // => Future[B] ! for { a <- fa b <- fb c <- longTimeC(a, b) } yield cToD(c) // => Future[D]

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ΞυϗοΫͳػೳ௥Ճ • ݺͼग़࣌͠ʹ͸ʮͦͷػೳ௥Ճ͞ΕͯΔ͔ʯ  νΣοΫ͕ίϯύΠϧ࣌ʹ૸Δ ← ܕ҆શ implicit class StringExt(val self: String) extends AnyVal { def suddenDeath = ??? } ! scala> "ಥવͷࢮ".suddenDeath res9: String = ʊਓਓਓਓਓਓʊ ʼɹಥવͷࢮɹʻ ʉY^Y^Y^Y^Yʉ

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ଞʹ΋ʮ͜Μͳػೳ͋Δʁʯ  ͱ͔͋Ε͹ڍ͍͛ͯͩ͘͞ʂ

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·ͱΊ

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Scalaͷྑ͍ͱ͜Ζ • ඼࣭Λॏࢹͨ͠։ൃ • ܕ͸υΩϡϝϯτ • ίϯύΠϧ͸ςετ • ΨνΨνʹݻΊͨ඼࣭ͷ࣮ݱΛ  ݴޠ͕ڧྗʹαϙʔτͯ͘͠ΕΔ • ϞμϯͳLLʹ΋Ҿ͚ΛͱΒͳ͍දݱྗ Speee Engineer’s Policy “COMPASS” ΑΓ

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͝੩ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠