Wrapping it up

We need to add additional behavior to the existing code so as to address cross-cutting concerns. Logging is a cross-cutting concern, for example. We have an existing method whose arguments we need to log without modifying the method itself. Don't worry, we have currying to the rescue! Here is how the code looks:

object WrapItUp extends App { 
  def attach_logger[X, Y](f: (X) => Y)(arg: X): Y = { // 1
    println("arg = " + arg.toString) 
    println("Calling the function...") 
    val result = f(arg)  // 2
    println("function call returned...") 	

    result 
  } 

  def f1(i: Integer): Integer = i + 10 // 3
  def f2(s: String): String = s + " " + s // 4

  val f1WithArgsLogged = attach_logger(f1) _ // 5 - attach argument loggin 
  val f2WithArgsLogged = attach_logger(f2) _ // without touching the function 

  println(s"Evaluating just f1 itself = ${f1(2)}\n") 
  println(s"Evaluating f1 with logging = ${f1WithArgsLogged(2)}\n") // 6
  println(s"Evaluating just f2 itself...