抽象类型type的使用

package currencies

/**
  * Created by jack on 2017/8/4.
  */
abstract class Currency {
  type CCurrency  <: Currency
  val mount:Long
  def designation:String
  def +(that:CCurrency):CCurrency = new CCurrency {
    this.mount + that.mount
  }
  def *(factor:Double):CCurrency  = new CCurrency {
    this.mount*factor
  }
}
class MyCurrency extends Currency {
  override type CCurrency = MyCurrency
  override val mount: Long = 100

  override def designation: String = "hello"
}



object NewCurrency extends App{

  val a = new MyCurrency()
  val b = new MyCurrency()
  val c = a+b
}

上面这段代码看起来没有任何问题，但是在执行“+”或者“*”操作的时候，编译无法通过，究其原因是因为scala不允许实例化一个type所代表的类型的对象，也就是上面

CCurrency所代表的类型，这是一个抽象的类型