Created
August 31, 2012 08:49
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難しいです
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lazy val fab: PartialFunction[Base, Int] = { | |
case A(base) => 1 + fabc(base) // PartialFunction#apply の呼び出し。危ない! | |
case B(left, right) => 1 + fabcd(left) + fabcd(right) // 同様 | |
} | |
// 全域関数だと scala コンパイラにはわからない! | |
lazy val fabcd: PartialFunction[Base, Int] = fab orElse { | |
case C => 1 | |
case D => 2 | |
} | |
// けど楽 | |
def impl(base: Base): Option[Int] = fab.lift(base) |
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lazy val fa: A => Int = { case A(base) => 1 + fabc(base) } | |
lazy val fb: B => Int = { case B(left, right) => 1 + fabcd(left) + fabcd(right) } | |
// 全域関数だと scala コンパイラにはわかる | |
lazy val fabcd: Base => Int = { | |
case A(_) @ a => fa(a) | |
case B(_) @ b => fb(b) | |
case C => 1 | |
case D => 2 | |
} | |
// コードの重複が… | |
def impl(base: Base): Option[Int] = Some(base).collect { | |
case A(_) @ a => fa(a) | |
case B(_) @ b => fb(b) | |
} |
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sealed trait Base | |
case class A(base: Base) extends Base | |
case class B(left: Base, right: Base) extends Base | |
case object C extends Base | |
case object D extends Base |
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