斯卡拉：告诉我一堂课需要抽象

Question

我跟随课程中的Scala课程并在其中一个视频中使用了以下代码：

 abstract class IntSet {
  def contains(x: Int): Boolean
  def incl(x: Int): IntSet
}

class Empty extends IntSet {
  def contais(x: Int): Boolean = false
  def incl(x: Int): IntSet = new NonEmpty(x, new Empty, new Empty)
  override def toString = "."
}

class NonEmpty(elem: Int, left: IntSet, right: IntSet) extends IntSet{
  def contains(x: Int): Boolean =
    if (x < elem) left contains x
    else if (x > elem) right contains x
    else true

  def incl(x: Int): IntSet =
    if (x < elem) new NonEmpty(elem, left incl x, right)
    else if (x > elem) new NonEmpty(elem, left, right incl x)
    else this

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

编译器告诉我：

 "Error:(6, 8) class Empty needs to be abstract, since method contains
 in class IntSet of type (x: Int)Boolean is not defined class Empty
 extends IntSet {
       ^"

根据其他posts，问题通常与方法签名中的不匹配有关，但在这种情况下＆＃34;包含＆＃34;在空中的签名与 IntSet 中的签名完全相同。

Answer 1

你写了一个错字：

class Empty extends IntSet {
  def contais(x: Int): Boolean = false

您键入了contais而不是contains。