通过非案例类的字段排序PriorityQueue(Ordering a PriorityQueue by a field of a non-case class)

 我目前正在尝试使用scala实现霍夫曼算法。 要做到这一点，我想我会使用PriorityQueue来根据它们的权重对树中不同节点的排序。 因此，我必须创建一个BinarySearchTree节点的PriorityQueue。 但是，Scala只允许我通过案例类的字段进行订购。 
 
 这是我想要的： 
 
  class BinarySearchTree(weight: Int)
  case class ForkNode(left: BinarySearchTree, right: BinarySearchTree, chars: List[Char], weight: Int) extends BinarySearchTree(weight)
  case class LeafNode(char: Char, weight: Int) extends BinarySearchTree(weight)

  def createBST(inputFile: ListMap[Char,Int]): BinarySearchTree = {
    def weightOrder(t2: BinarySearchTree) = t2.weight
    val nodeMap:PriorityQueue[BinarySearchTree] = PriorityQueue(Ordering.by(weightOrder))
    null
  }
 
 但它不编译。 但是， def weightOrder(t2: ForkNode) = t2.weight不会编译，但这不是我想要的。 
 
 我如何根据非案例类中的字段来排序我的优先级队列？ 

I'm currently trying to implement the huffman algorithm using scala. To do this, I'd figured I'd use a PriorityQueue for the ordering of the different Nodes in the tree based on their weight. Thus, I have to create a PriorityQueue of BinarySearchTree Nodes. However, Scala only lets me order by a field of a case class.
 
This is want I want:
 
  class BinarySearchTree(weight: Int)
  case class ForkNode(left: BinarySearchTree, right: BinarySearchTree, chars: List[Char], weight: Int) extends BinarySearchTree(weight)
  case class LeafNode(char: Char, weight: Int) extends BinarySearchTree(weight)

  def createBST(inputFile: ListMap[Char,Int]): BinarySearchTree = {
    def weightOrder(t2: BinarySearchTree) = t2.weight
    val nodeMap:PriorityQueue[BinarySearchTree] = PriorityQueue(Ordering.by(weightOrder))
    null
  }
 
But it doesn't compile. However, def weightOrder(t2: ForkNode) = t2.weight does compile, but that is not what I want.
 
How can I order my priority queue based on a field in a non-case class?

原文：https://stackoverflow.com/questions/47043379