Benchmark anonymous function creation in Scala

benchmark_23737147.scala

/**
Benchmark for the question "For comprehension and number of function creation" on SO. (http://stackoverflow.com/q/23737147/108915)

Answer: http://stackoverflow.com/a/23742289/108915
*/

object M {

    def useIt(): Unit = {
        println(variantA())
        println(variantB())
        println(variantC())
        println(variantD())
    }

    def time(f: () => Unit,n: Int): Unit = {
        val now = System.nanoTime()
        var i = 0
        while(i<n){
            f()
            i+=1
        }
        println((System.nanoTime() - now)*1e-9)
    }

    val matrix = IndexedSeq.tabulate(1000, 1000) { case (x, y) => x + y }

    def main(args: Array[String]): Unit = {
        println("A")
        for(_ <- 1 to 5) time(() => variantA,500)
        println("B")
        for(_ <- 1 to 5) time(() => variantB,500)
        println("C")
        for(_ <- 1 to 5) time(() => variantC,500)
        println("D")
        for(_ <- 1 to 5) time(() => variantD,500)

        println("verify results")
        useIt()
    }
    
    def variantA(): Int = {
        var r = 0
        for {
           row <- matrix
           elem <- row
        }{
           r += elem
        }
        r
    }
    def variantB(): Int = {
        var r = 0
        val f = (x:Int) => r += x
        for {
           row <- matrix
           elem <- row
        } f(elem)
        r
    }
    def variantC(): Int = {
        var r = 0
        var i1 = 0
        while(i1 < matrix.size){
            var i2 = 0
            val row = matrix(i1)
            while(i2 < row.size){
                r += row(i2)
                i2 += 1
            }
            i1 += 1
        }
        r
    }
    def variantD(): Int = matrix.foldLeft(0)(_ + _.sum)
}