Implicit classes in Scala are an underused and oft misused feature. I don’t feel that they are explained very well and have a bit too much mystery for the beginner to grasp. I was playing around and thought it might help to show the explicit syntax, to more easily explain the “magic” to someone.

In a nutshell:

import scala.language.postfixOps

object Factorial {

  implicit class IntDecorator(val n: Int) {
    def ! = 1 to n product
  }

  def factorial(n: Int) =  n!                 // implicit

  def factorial2(n: Int) = IntDecorator(n).!  // explicit

}