ArrayMap.scala

ArrayMap.scala

trait EnumMap[A, B] {
  def apply(a: A): B
}

// Quick sketch, untested.
final class ArrayEnumMap[A, @spec B : ClassTag](xs: Seq[(A,B)]) extends EnumMap[A,B] {

  val (keys, values) = mkEntries(xs)
  val size = keys.length

  def mkEntries(xs: Seq[(A,B)]): (Array[Int], Seq[B]) = {
    val sorted = xs.sortBy(_._1.hashCode)
    (sorted.map(_._1.hashCode).toArray, sorted.map(_._2))
  }

  @inline
  def apply(a: A) = {
    val hash = a.hashCode

    var high = size
    var low = 0
    var i  = (high - low) >> 1

    while (hash != keys(i) && high != low) {
      if (hash < keys(i)) high = i else low = i

      i  = low + ((high - low) >> 1)
    }

    values(i)
  }

}

object ArrayEnumMap {
  def apply[A, @spec B : ClassTag](xs: (A,B)*) = new ArrayEnumMap(xs)
}