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如何访问类参数?

scala

0

Milo Lu · 技术社区 · 7 年前

Scala编程 ,第304页

class Queue[T] private (leading: List[T], trailing: List[T]){
  private def mirror =
    if(leading.isEmpty) new Queue(trailing.reverse, Nil)
    else this
  def head = mirror.leading.head
  def tail = {
    val q = mirror
    new Queue(q.leading.tail, q.trailing)
  }
  def append[T](x: T)={
    new Queue(leading, x::trailing)
  }
}

我得到以下错误

Error:value leading is not a member of Queue[T]
def head = mirror.leading.head

trailing . mirror Queue 正当为什么它不能访问它的类参数?

1 回复 | 直到 7 年前

1

2

yÇsÊÇla 7 年前

的确 leading 和 trailing Queue 类,但默认情况下它们是私有的。要使其公开,请添加 val

之前:

scala> class Queue[T] private (leading: List[T], trailing: List[T]){
     |   private def mirror =
     |     if(leading.isEmpty) new Queue(trailing.reverse, Nil)
     |     else this
     |   def head = mirror.leading.head
     |   def tail = {
     |     val q = mirror
     |     new Queue(q.leading.tail, q.trailing)
     |   }
     |   def append[T](x: T)={
     |     new Queue(leading, x::trailing)
     |   }
     | }
<console>:15: error: value leading is not a member of Queue[T]
         def head = mirror.leading.head
                           ^
<console>:18: error: value leading is not a member of Queue[T]
           new Queue(q.leading.tail, q.trailing)
                       ^
<console>:18: error: value trailing is not a member of Queue[T]
           new Queue(q.leading.tail, q.trailing)
                                       ^

之后:

scala> class Queue[T] private (val leading: List[T], val trailing: List[T]){
     |   private def mirror =
     |     if(leading.isEmpty) new Queue(trailing.reverse, Nil)
     |     else this
     |   def head = mirror.leading.head
     |   def tail = {
     |     val q = mirror
     |     new Queue(q.leading.tail, q.trailing)
     |   }
     |   def append[T](x: T)={
     |     new Queue(leading, x::trailing)
     |   }
     | }
defined class Queue

您可以详细阅读构造函数和getter here

瓦尔 或 var 这个班。