method-dependent-types なくても普通に返値型は変えられますよの話

todate.scala

def toDate[Result](magnet: DateMagnet[Result]): Result = magnet.convert

trait DateMagnet[Result] {
  def convert(): Result
}

object DateMagnet {
  implicit def fromInt(tuple:(Int, Int, Int)) = new DateMagnet[java.util.Calendar] {
    def convert() = {
      val (year, month, date) = tuple
      val c = java.util.Calendar.getInstance
      c.set(year, month - 1, date, 0, 0, 0)
      c
    }
  }

  implicit def fromString(s:String) = new DateMagnet[java.util.Date] {
    def convert() = new java.text.SimpleDateFormat("yyyy/MM/dd").parse(s)
  }
}