Some observations on performance (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
	**/

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