带有循环的Scala不可变链表

Question

在 Scala 中，我需要用循环创建一个不可变的链表。就像是:

case class Node(element: Int, next: Node)
val linkedList = Node(1, Node(2, null))
val cycle = Node(3, cycle)

cycle.next // this should go back to the same element

但它不起作用。如何使用循环制作不可变链表？

Answer 1

使用惰性值和按名称参数来推迟初始化:

class Node(val element: Int, next_ : => Node) {
  lazy val next = next_
}

lazy val root: Node =
  new Node(1,
    new Node(2,
      new Node(3, root)
    )
  )

// tail-recursive print function as a bonus
def printRec(node: Node, depth: Int): Unit = if (depth > 0) {
  println(node.element)
  printRec(node.next, depth - 1)
}

printRec(root, 10)

输出:

1
2
3
1
2
3
1
2
3
1