文字列をサロゲートペアを考慮した1文字ずつに分割する

gistfile1.scala

object SurrogatePair {

  case class Pair(x: Char, y: Option[Char] = None) {
    lazy val surrogatePair = y match {
      case None => false
      case Some(yy) => Character.isSurrogatePair(x, yy)
    }

    lazy val text = surrogatePair match {
      case true => x.toString + y.get
      case false => x.toString
    }
  }

  def split(target: String): Seq[String] = {
    target.length match {
      case 0 => Seq()
      case 1 => Seq(target)
      case _ => {
        val pairs = {
          (0 until target.length - 1) map {
            i =>
              Pair(target(i), Some(target(i + 1)))
          }
        } :+ Pair(target(target.length - 1))
        (0 until pairs.length) flatMap {
          i =>
            if (i > 0 && pairs(i - 1).surrogatePair) {
              None
            } else {
              Some(pairs(i).text)
            }
        }
      }
    }
  }

}