time a scala expression's execution

timer.scala

// e.g., from the repl:
//    scala> :load timer.scala
//    [...]
//    scala> timed(Thread.sleep(1000))
//    took 1001606189ns (1001ms)

def timed[T](block: => T): T = {
  import java.time.Duration

  val startTime = System.nanoTime()
  val res = block
  val endTime = System.nanoTime()
  val took = Duration.ofNanos(endTime - startTime)
  println(s"took ${took.toNanos}ns (${took.toMillis}ms)")
  res
}