• A Higher-Order function is a function that does at least one of the following:

  • Takes one or more functions as an input
  • Outputs a function

• In example below, there is a function: apply which takes another function f and a value v and applies function f to v

• Function: apply consumes an Int and returns a String : Int => String

• In example below, method decorator.layout is coerced automatically to a value of type Int => String as required by method apply

object HighOrderFunctionTest extends App {

  /* Method `apply` has two params: function `f` & value `v` and it applies `f` to `v` */
  def apply(f: Int => String, v: Int) = f(v)

  /* Create a new 'Decorator' object */
  val decorator = new Decorator("[", "]")

  /* Pass 'decorator.layout' to 'apply' */
  val layoutOutput = apply(decorator.layout, 7)

  println(layoutOutput)
}

class Decorator(left: String, right: String) {

  /* Method is bound to type 'A' */
  def layout[A](x: A) = left + x.toString() + right
}