Scala 末尾再帰とループとfoldのベンチマーク

bench.scala

import scala.testing.Benchmark
import scala.annotation.tailrec

trait Times {
  def times(elems: Seq[BigInt]): BigInt
}

abstract class Bench extends Times with Benchmark {
  val fixture = BigInt(1) to BigInt(2000)
  def run() { times(fixture) }
}

object Tail extends Bench {
  def times(elems: Seq[BigInt]): BigInt = {
    @tailrec
    def worker(b: BigInt, s: Seq[BigInt]): BigInt = {
      if (s.isEmpty) b else worker(b * s.head, s.tail)
    }
    worker(BigInt(1), elems)
  }
}

object Loop extends Bench {
  def times(elems: Seq[BigInt]): BigInt = {
    var res = BigInt(1)
    elems foreach { res *= _ }
    res
  }
}

object Fold extends Bench {
  def times(elems: Seq[BigInt]): BigInt = {
    (BigInt(1) /: elems){ _ * _ }
  }
}

object Main {
  def main(args: Array[String]) {
    // test
    test(Tail)
    test(Loop)
    test(Fold)

    // benchmark
    Tail.main(args)
    Loop.main(args)
    Fold.main(args)
  }

  def test(t: Times) {
    assert{ t.times(BigInt(1) to BigInt(0)) == BigInt(1) }
    assert{ t.times(BigInt(1) to BigInt(1)) == BigInt(1) }
    assert{ t.times(BigInt(1) to BigInt(2)) == BigInt(2) }
    assert{ t.times(BigInt(1) to BigInt(3)) == BigInt(6) }
  }
}