4

这是我的文件

trait Set[T] {
    def contains(x: T): Boolean
    def incl(x: T): Set[T]
    def union(that: Set[T]): Set[T]
}

class Empty[T] extends Set[T] {
    override def toString = "."
    def contains(x: T): Boolean = false
    def incl(x: T): Set[T] = new NonEmpty[T](x, new Empty[T], new Empty[T])
    def union(that: Set[T]): Set[T] = that
}

class NonEmpty[T](elem: T, left: Set[T], right: Set[T]) extends Set[T] {
    override def toString = "{" + left + elem + right + "}"

    def contains(x: T): Boolean =
        if (x < elem) left contains x
        else if (x > elem) right contains x
        else true

    def incl(x: T): Set[T] =
         if (x < elem) new NonEmpty(elem, left incl x, right)
         else if (x > elem) new NonEmpty(elem, left, right incl x)
         else this

    def union(that: Set[T]): Set[T] =
        ((left union right) union that) incl elem
}

我正在使用 ":paste" 方法,因为 :load 不起作用。但我收到以下错误

<console>:25: error: value < is not a member of type parameter T
               if (x < elem) left contains x
                     ^
<console>:26: error: value > is not a member of type parameter T
               else if (x > elem) right contains x
                          ^
<console>:30: error: value < is not a member of type parameter T
                if (x < elem) new NonEmpty(elem, left incl x, right)
                      ^
<console>:31: error: value > is not a member of type parameter T
                else if (x > elem) new NonEmpty(elem, left, right incl x)

我确定这个文件是正确的,因为它来自课堂示例,并且在教授使用时它在课堂上工作......

有什么帮助吗?

4

2 回答 2

5

您会收到该错误,因为并非每种类型T都定义了><

您可能想要的是T或者Ordered可以隐式转换为 is 的东西,Ordered因此定义了所有的东西。

这应该修复错误消息:

class NonEmpty[T <% Ordered[T]](elem: T, left: Set[T], right: Set[T]) extends Set[T] {
    override def toString = "{" + left + elem + right + "}"

    def contains(x: T): Boolean =
        if (x < elem) left contains x
        else if (x > elem) right contains x
        else true

    def incl(x: T): Set[T] =
        if (x < elem) new NonEmpty(elem, left incl x, right)
        else if (x > elem) new NonEmpty(elem, left, right incl x)
        else this

    def union(that: Set[T]): Set[T] =
        ((left union right) union that) incl elem
}

T <% S(视图绑定)说 typeT必须可转换为S,因此它必须是 的子类型S或已定义隐式转换。

接受者对此问题的回答更详细地解释了它。

于 2013-05-12T10:35:45.270 回答
0

由于“视图边界”在 Scala 2.11 中已被弃用,使用“上下文边界”的通用二叉搜索树的替代实现如下:

object GenericBinarySearchTree {

abstract class Set[T] {
  def incl(x: T): Set[T]
  def contains(x: T): Boolean
  def union(that: Set[T]): Set[T]
}

type L[X] = X => Ordered[X]

class Empty[T : L] extends Set[T] {

  override def toString = "."

  def incl(x: T): Set[T] = new NonEmpty(x, new Empty, new Empty)

  def contains(x: T): Boolean = false

  def union(that: Set[T]): Set[T] = that
}

class NonEmpty[T : L](elem: T, left: Set[T], right: Set[T]) extends Set[T] {  

  override def toString = "{" + left + elem + right + "}"

  def incl(x: T): Set[T] = {
    if(x > elem) new NonEmpty(elem, left, right.incl(x))
    else if(x < elem) new NonEmpty(elem, left.incl(x), right)
    else this
  }

  def contains(x: T): Boolean = {
    if(x == elem) true 
    else if(x > elem) right.contains(x)
    else left.contains(x)
  } 

  def union(that: Set[T]): Set[T] = ((left union right) union that) incl elem
}

}
于 2016-08-13T06:42:02.803 回答