表现 – Scala的.min如何避免拳击和开箱的惩罚？

def min[B >: A](implicit cmp: Ordering[B]): A = {
  if (isEmpty)
    throw new UnsupportedOperationException("empty.min")
  reduceLeft((x,y) => if (cmp.lteq(x,y)) x else y)
}

当你的个人资料

Vector.fill(1000000)(scala.util.Random.nextLong).min

它很快,没有拳击或拆箱.但是,如果你写出这个相当的代码

val cmp = implicitly[Ordering[Long]]
Vector.fill(1000000)(scala.util.Random.nextLong).reduceLeft((x,y)) x else y)

它运行速度大约减慢了10倍(忽略了随机时间,否则主导了这一点,是的,我加热了我的基准…).

How is the first version avoiding the performance penalty of the boxing?

编辑：这是我的分析代码：

val cmp = implicitly[Ordering[Long]]

def randomLongs = Vector.fill(1000000)(scala.util.Random.nextLong)

def timing[R](f: => R): (Long,R) = {
  val startTime = System.nanoTime
  val result = f
  ((System.nanoTime - startTime) / 1000000,result)
}

def minTiming = { val r = randomLongs; timing(r.min)._1 }
def reduceLeftTiming = { val r = randomLongs; timing(r.reduceLeft((x,y)) x else y))._1 }

while(true) {
  println((minTiming,reduceLeftTiming))
}

我看到时间使用最小约20ms,使用?200ms的reduceLeft.我使用YourKit对这段代码进行了分析;这是一个screen grab的呼叫树,显示min不会导致任何拳击.