Performance (Scala)

gistfile1.scala

package performance

import java.util.Date

/**
 * In this little demo we try to calculate the sum of a list of numbers (0,1,... ,1000.000) 
 * using various approaches. As we will see Java outperforms the Scala versions with just
 * a few milliseconds at the expense of readability, maintainability and productivity.
 * 
 * However, I noticed that passing a method instead of a function comes with a performance penalty. 
 * In that case the method is converted to a function using ETA expansion. 
 */ 
object SumUp extends App {

  
  val numbers = (0 to 1000000).toList
  
  def sumJava(numbers: List[Int]):Int =  {
    var total = 0
    for (number <- numbers) {
      total = total + number
    }
    total
  }
  
  def sumScala1(numbers: List[Int]):Int =  numbers.foldLeft(0)((a,b) => a + b)
  def sumScala2(numbers: List[Int]):Int =  numbers.foldLeft(0)(sum)
  def sumScala3(numbers: List[Int]):Int =  numbers.foldLeft(0)(sumAsFunction)
  def sumScala4(numbers: List[Int]):Int =  numbers.foldLeft(0)(new SumFunction)
  
  def sum(a: Int, b: Int): Int = a + b
  
  val sumAsFunction = sum _  //here we convert the method to a function
  
  class SumFunction extends Function2[Int,Int, Int] {
    def apply(a: Int, b: Int): Int = a + b
  }
  
  
  /**
   * profile method works like an Around Advice in AspectOriented programming
   */
  def profile[T](body: => T) = {
      val start = new Date()
      val result = body
      val end = new Date()
      println("Execution took " + (end.getTime() - start.getTime()) + " milliseconds")
      result
  }
  

  profile(sumJava(numbers))    //using imperative Java
  profile(sumScala1(numbers))  //using inline function 
  profile(sumScala2(numbers))  //using method
  profile(sumScala3(numbers))  //using method converted to function before passing it to foldleft
  profile(sumScala4(numbers))  //using a function class
  
}


/**
Execution took 14 milliseconds   //using imperative Java
Execution took 17 milliseconds   //using inline function
Execution took 95 milliseconds   //using method
Execution took 17 milliseconds   //using method converted to function 
Execution took 18 milliseconds   //using a function class
**/