一个特设多态的小例子

ListenerEvent是某个库的类, 想要转化为它所代表的的ddl操作,通过implicit, 存在类型(通过定义T2DDL改成了上下文限定), 完成了特设多台

trait ToDDLModification[T <: ListenerEvent] {
  def toDDLModification: DDLModification
}

object ToDDLModification{

  type T2DDL[X] = X => DDLModification

  implicit class ToDDL[T <: ListenerEvent : T2DDL](event: T) extends ToDDLModification[T] {
    override def toDDLModification: DDLModification = {
      implicitly[T2DDL[T]].apply(event)
    }
  }

  implicit val alterParFunc: T2DDL[AlterPartitionEvent] = e => {
   DDLModification("")
  }

  implicit val createDbFunc: T2DDL[CreateDatabaseEvent] = e => {
   DDLModification("")
  }
}