function composition

gistfile1.scala

abstract class PrintSomething() {
  def apply(s: String): Unit
}

object PrintSomething {

  /**
   * @param printMethod a method that prints something
   * @return a PrintSomething with an apply method
   * equal to your printMethod
   */
  def build(printMethod: (String) => Unit): PrintSomething =
    new PrintSomething() {
      def apply(s: String) = printMethod(s)
    }

  /**
   * Create a PrintSomething that is actually
   * a composition of many PrintSomethings
   *
   * @param printers a sequence of printers
   * @return a PrintSomething with an apply method
   * that executes each printer you passed in
   */
  def compose(printers: Seq[PrintSomething]): PrintSomething =
    build((s) => printers.foreach { p => p(s) })
}

val printer1 = PrintSomething.build((s) => print("\nI love " + s))

val printer2 = PrintSomething.build((s) => print("\nI hate " + s))

val multiPrinter = PrintSomething.compose(Seq(printer1, printer2))

printer1("cats")
// I love cats

printer2("cats")
// I hate cats

multiPrinter("cats")
// I love cats
// I hate cats