如何在scala中的对象内使用方法？(how to use method inside an object in scala?)

 我在scala工作表中有这个示例代码。 我不明白为什么我无法访问代码底部的函数。 
 
object chapter5 {
  println("Welcome to the Scala worksheet")

  trait Stream2[+A] {
    def uncons: Option[(A, Stream2[A])]
    def isEmpty: Boolean = uncons.isEmpty
  }
  object Stream2 {

    def empty[A]: Stream2[A] =
      new Stream2[A] { def uncons = None }

    def cons[A](hd: => A, tl: => Stream2[A]): Stream2[A] =
      new Stream2[A] {
        lazy val uncons = Some((hd, tl))
      }

    def  apply[A](as: A*): Stream2[A] =
      if (as.isEmpty) empty
      else cons(as.head, apply(as.tail: _*))
  }

  val s = Stream2(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    s.isEmpty //I can access to the function declared in the trait
    s.cons // error  // I can not access to the function declared in the object
}
 
 另外我需要编写toList方法。 我应该在哪里写呢？ 如果我无法访问这些方法，我该如何测试呢？ 

I have this sample code in a scala worksheet. I do not understand why I can not access to the functions as at the bottom of the code. 
 
object chapter5 {
  println("Welcome to the Scala worksheet")

  trait Stream2[+A] {
    def uncons: Option[(A, Stream2[A])]
    def isEmpty: Boolean = uncons.isEmpty
  }
  object Stream2 {

    def empty[A]: Stream2[A] =
      new Stream2[A] { def uncons = None }

    def cons[A](hd: => A, tl: => Stream2[A]): Stream2[A] =
      new Stream2[A] {
        lazy val uncons = Some((hd, tl))
      }

    def  apply[A](as: A*): Stream2[A] =
      if (as.isEmpty) empty
      else cons(as.head, apply(as.tail: _*))
  }

  val s = Stream2(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    s.isEmpty //I can access to the function declared in the trait
    s.cons // error  // I can not access to the function declared in the object
}
 
In addition I need to write the toList method. Where should I write it? How can I test it if I can not access to the methods ?

原文：https://stackoverflow.com/questions/28860279