如何解决scala中的类型不匹配

Question

我需要在scala中使用此代码一些帮助，我想实现foldL方法，但即时通讯得到了

asd.scala:73: error: type mismatch;
 found   : Option[MyTree[A]] => B
 required: B
      def myFoldLeft[B](z: B)(op: (B, A) => B): B = (_:Option[MyTree[A]]) match {
                                                                          ^
one error found

我知道多数民众赞成在类型不匹配，但我与斯卡拉和面向对象的新手，我不 了解如何解决这种情况。

class MyTree[A](val value: A, val left:Option[MyTree[A]],
                              val right:Option[MyTree[A]]) {

  def myFoldLeft[B](z: B)(op: (B, A) => B): B = (_:Option[MyTree[A]]) match {
    case Some(tree) => right.get.myFoldLeft (left.get.myFoldLeft (op(z, value)) (op)) (op)
    case None => z
  }
}

Answer 1

(_:Option[MyTree[A]]) ...是lambda。

您应该像这样

class MyTree[A](val value: A, val left:Option[MyTree[A]],
                val right:Option[MyTree[A]]) {    
  def myFoldLeft[B](z: B)(op: (B, A) => B): B = (left, right) match {
    case (Some(left), Some(right)) => ???
    case (Some(left), None) => ???
    case (None, Some(right)) => ???
    case (None, None) => ???
  }
}