Question

这些代码汇编得很好：

  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


  def weight(tree: CodeTree): Int = tree match {
    case Fork(left, right, chars, weight) => weight
    case Leaf(char, weight) => weight
  }

  def insert_orderedCodeTreeList[T >: CodeTree](leaf: CodeTree, orderedCodeTrees: List[CodeTree]): List[T] = orderedCodeTrees match {
    case Nil => List(leaf)
    case head :: tail => {
      if (weight(leaf) <= weight(head)) leaf :: orderedCodeTrees
      else head :: insert_orderedCodeTreeList(leaf, tail)
    }
  }

但是当我像这样使用它时会抛出错误：

insert_orderedCodeTreeList[Leaf](Leaf(theChar, theInt), makeOrderedLeafList(tail))

type arguments [patmat.Huffman.Leaf] do not conform to method insert_orderedCodeTreeList's type parameter bounds [T >: patmat.Huffman.CodeTree]
[error]     case (theChar, theInt) :: tail => insert_orderedCodeTreeList[Leaf](Leaf(theChar, theInt), makeOrderedLeafList(tail))
[error]                                                                 ^
[error] one error found

可以看出，类型参数T使用CodeTree作为下限，因此，我认为在{{的参数列表中用T替换CodeTree可能没问题。 1}}：

insert_orderedCodeTreeList

然而，编译器抱怨说：

  def insert_orderedCodeTreeList[T >: CodeTree](leaf: T, orderedCodeTrees: List[T]): List[T] = orderedCodeTrees match {
    case Nil => List(leaf)
    case head :: tail => {
      if (weight(leaf) <= weight(head)) leaf :: orderedCodeTrees
      else head :: insert_orderedCodeTreeList(leaf, tail)
    }
  }

有没有人有这方面的想法？

Answer 1

在阅读the document about bounds后，我发现正确的方法是这样写：

  def insert_orderedCodeTreeList[T <: CodeTree](leaf: T, orderedCodeTrees: List[T]): List[T] = orderedCodeTrees match {
    case Nil => List(leaf)
    case head :: tail => {
      if (weight(leaf) <= weight(head)) leaf :: orderedCodeTrees
      else head :: insert_orderedCodeTreeList(leaf, tail)
    }
  }

在scala中，为什么这里没有很好地降低工作量？

1 个答案: