Scala发散隐式扩展编译器错误

Question

Can someone help me understand the compile error message below? I've been looking at this for a while now and I don't understand what's wrong.

  def makeOrderedLeafList(freqs: List[(Char, Int)]): List[Leaf] = {
    val buff = ListBuffer[Leaf]();
    for(u<-freqs) {
       val v = new Leaf(u._1, u._2)
       buff += v
    }
    buff.toList.sortBy(_.weight) //<= offending line
  }

Error message:

diverging implicit expansion for type scala.math.Ordering[B] starting with method Tuple9 in object Ordering

EDIT: Class declarations look like:

  abstract class CodeTree
  case class Fork(left: CodeTree, right: CodeTree, chars: List[Char], weight: Int) extends CodeTree
  case class Leaf(char: Char, weight: Int) extends CodeTree

Answer 1

Works for me on scala 2.10.0

import scala.collection.mutable._

then paste in the code you supply above. makeOrderedLeafList compiles without error and seems to work in the intended way:

scala> makeOrderedLeafList(List(('a',8),('b',9),('c',99),('d',1)))
res0: List[Leaf] = List(Leaf(d,1), Leaf(a,8), Leaf(b,9), Leaf(c,99))