如何解决scala中的类型不匹配

Question

我需要一些有关 Scala 中这段代码的帮助，我想实现 foldL 方法，但我得到了这个：

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

我知道这是一个类型不匹配，但我是 scala 和 Oriented Object 的新手，我不知道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]]) ... 是一个 lambda。

你应该匹配

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) => ???
  }
}

如何解决scala中的类型不匹配

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