尝试在List上定义新的隐式方法时出错

Question

我试图使用以下代码添加newMethod在List类上调用的方法.

implicit class ListCompanionOps(f: List.type) extends AnyVal {
  def newMethod(p: String) = {
    println(p)
  }
}

但编译器抱怨以下错误:

$ scalac test.scala
test.scala:3: error: ListCompanionOps is already defined as (compiler-generated) method ListCompanionOps
implicit class ListCompanionOps(f: List.type) extends AnyVal {
               ^
one error found

我究竟做错了什么？

谢谢

Answer 1

它应该是:

implicit class ListCompanionOps[A](val f: List[A]) extends AnyVal {

List.type将意味着一些被称为对象的类型List.