我有一个函数，我希望它是通用的，但限制它采取某些子类型。为了简单起见，我希望我的函数只处理long、int、float和double。所以我想到的是：

def covariance[A](xElems: Seq[A], yElems: Seq[A]): A = {
  val (meanX, meanY) = (mean(xElems), mean(yElems))
  val (meanDiffX, meanDiffY) = (meanDiff(meanX, xElems), meanDiff(meanY, yElems))
  ((meanDiffX zip meanDiffY).map { case (x, y) => x * y }.sum) / xElems.size - 1
}

def mean[A](elems: Seq[A]): A = {
  (elems.fold(_ + _)) / elems.length
}

def meanDiff[A](mean: A, elems: Seq[A]) = {
  elems.map(elem => elem - mean)
}

以下是我将用于检查上述类型的方法：

import scala.reflect.{ClassTag, classTag}
def matchList2[A : ClassTag](list: List[A]) = list match {
  case intlist: List[Int @unchecked] if classTag[A] == classTag[Int] => println("A List of ints!")
  case longlist: List[Long @unchecked] if classTag[A] == classTag[Long] => println("A list of longs!")
}

注意，我使用的是classtag。我也可以使用一个typetag，甚至可以使用这个不成形的库。
我想知道这是不是一个好办法？或者我应该使用有界类型来解决我想要的问题？
编辑：基于对使用fractional typeclass的评论和建议，下面是我认为它是如何工作的！

def covariance[A: Fractional](xElems: Seq[A], yElems: Seq[A]): A = {
  val (meanX, meanY) = (mean(xElems), mean(yElems))
  val (meanDiffX, meanDiffY) = (meanDiff(meanX, xElems), meanDiff(meanY, yElems))
  ((meanDiffX zip meanDiffY).map { case (x, y) => x * y }.sum) / xElems.size - 1
}

def mean[A](elems: Seq[A]): A = {
  (elems.fold(_ + _)) / elems.length
}

def meanDiff[A](mean: A, elems: Seq[A]) = {
  elems.map(elem => elem - mean)
}