ʢ༨ஊʣཏੑνΣοΫ 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.
͞ΕͨOptionΛѻ͏ val found: Option[A] = aList.find(condition) ! // BAD (ݹ͖ྑ͖nullνΣοΫͱҰॹ) if (found.isDefined) { val a = found.get ??? } ! // So so ... (લड़ͷཏੑνΣοΫΔ) found match { case Some(a) => ??? case None => ??? }
OptionʹؔΛ͢ // 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]
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 => ??? }
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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