What does Node [TypeOne <: Node [TypeOne]] mean in scala?

Question

I can’t understand how this code works?

class Node[TypeOne <: Node[TypeOne]] {
  var x: TypeOne = _
}


object Tree extends App {
  val treeNode = new Node[String]
  treeNode.x = "ten"
  //treeNode.x = new TreeNode[String]
}

I originally thought of the Node signature class [TypeOne <: Node [TypeOne]], it meant that any type x variable of type TypeOne should be of type Node or its subclass, but it doesn't seem like that, since I can create a val treeNode of type Node [ String] and Node [Int]. So what does this signature do?

Answer 1

This pattern is usually used for base classes or features that want to know their specific subtype statically. Most likely, the library designer expects you to continue Node:

class MyNode extends Node[MyNode]

MyNode Node.

Answer 2

" " scala. , , , :

• twitter scala : https://twitter.imtqy.com/scala_school/advanced-types.html
• wikipedia: https://en.wikipedia.org/wiki/Bounded_quantification
• http://blog.originate.com/blog/2014/02/27/types-inside-types-in-scala/