在scala中扩展trait时，如何创建新的特定类型的类

我有一个特点（除其他外）我需要一个方法来创建一个新的类实例，然后还有其他方法使用该类实例

我的代码有一个非常精简的版本：

trait A {
  def prev: A
  def get(end: A): A
}

class B extends A {
  def prev: B = new B()
  def get(end: B): B = end.prev
}

我在这里试图说明的是，next将返回类的一个新实例（实际上带有一些新的构造函数参数），get方法将在内部使用next（以及其他逻辑）

上面的问题是编译器说“类B必须实现抽象成员get（end:A）：A”，这是合理的

我尝试使用类型边界来解决它，如下所示：

trait A {
  def prev: A
  def get(end: A): A
}

case class B extends A {
  def prev[TX <: A]: TX = new B()
  def get[TX <: A](end: TX): TX = end.prev
}

我的班级看起来像：

case class Node[T](val data: T, var prev: Node[T], var next: Node[T])

case class CircularList[T](first: Node[T], last: Node[T], current: Node[T]) 
  extends Circular[T] {

  // Nodes in the list from the current position up to but not including the end
  def toStream(end: CircularList[T]): Stream[CircularList[T]] = {
    @tailrec
    def toStreamRec(end: CircularList[T], acc: Stream[CircularList[T]]): Stream[CircularList[T]] = {
      if (this == end) {
        acc
      } else {
        toStreamRec(end.prev, Stream.cons(end.prev, acc))
      }
    }
    toStreamRec(end, Stream.empty)
  }

  def prev: CircularList[T] = new CircularList[T](first, last, current.prev)
  ...

---

因此，在我的简化示例中，

toStream

映射到

get

。

您需要的是一个名为。代码如下所示：

trait Base[T <: Base[T]] {
  def next: T
  def get(end: T): T
}

class Chlid extends Base[Child] {
  def next: Chlid = new Chlid()
  def get(end: Chlid): Chlid = end.next
}

不是对的覆盖

def get(end: A): A

因为原始方法接受类型为

A

的对象，而您的方法只需要更窄的类型

B

---

对于您的

循环

示例，您希望

trait Circular[T, C <: Circular[T, C]] {
  // Nodes in the list from the current position up to but NOT INCLUDING the end
  def toStream(end: C): Stream[C]

  def next: C
}

case class Node[T](val data: T, var prev: Node[T], var next: Node[T])

case class CircularList[T](first: Node[T], last: Node[T], current: Node[T]) extends Circular[T, CircularList[T]] {

  // Nodes in the list from the current position up to but not including the end
  def toStream(end: CircularList[T]): Stream[CircularList[T]] = {
    @tailrec
    def toStreamRec(end: CircularList[T], acc: Stream[CircularList[T]]): Stream[CircularList[T]] = {
      if (this == end) {
        acc
      } else {
        toStreamRec(end.prev, Stream.cons(end.prev, acc))
      }
    }

    toStreamRec(end, Stream.empty)
  }

  def prev: CircularList[T] = new CircularList[T](first, last, current.prev)

  override def next: CircularList[T] = ???
}

---

trait循环[T，C谢谢！这为我节省了大量时间。
def get(end: A): A

trait Circular[T, C <: Circular[T, C]] {
  // Nodes in the list from the current position up to but NOT INCLUDING the end
  def toStream(end: C): Stream[C]

  def next: C
}

case class Node[T](val data: T, var prev: Node[T], var next: Node[T])

case class CircularList[T](first: Node[T], last: Node[T], current: Node[T]) extends Circular[T, CircularList[T]] {

  // Nodes in the list from the current position up to but not including the end
  def toStream(end: CircularList[T]): Stream[CircularList[T]] = {
    @tailrec
    def toStreamRec(end: CircularList[T], acc: Stream[CircularList[T]]): Stream[CircularList[T]] = {
      if (this == end) {
        acc
      } else {
        toStreamRec(end.prev, Stream.cons(end.prev, acc))
      }
    }

    toStreamRec(end, Stream.empty)
  }

  def prev: CircularList[T] = new CircularList[T](first, last, current.prev)

  override def next: CircularList[T] = ???
}