factorial.scala

object UsingExt {
  import Ext._

  def factTwice(n: Int): BigInt = (n!)!

}

object Ext {

  implicit class Ops(n: Int) {
    def !(): BigInt = (1 to n).foldLeft(BigInt(1))(_ * _)
  }

  implicit class OpsBig(n: BigInt) {
    def !(): BigInt = Ops(n.toInt)!
  }

}