Question

我指的是发布在Scala implicit conversion for object

中的答案

sealed trait Command {
  val typeName: String
  //This is required for implicit conversion.
  override def toString: String = typeName
}

object SendMessageCommand extends Command {
  override val typeName: String = "send_message"
}
object AddMessageCommand extends Command {
  override val typeName: String = "add_message1"
}
object UpdateMessageCommand extends Command {
  override val typeName: String = "update_message"
}
object DeleteMessageCommand extends Command {
  override val typeName: String = "delete_message"
}

//List of commands.
implicit val cmds: List[Command] = List(SendMessageCommand, AddMessageCommand, UpdateMessageCommand, DeleteMessageCommand)

//Convert given type T into type U.
implicit def convert[T, U](s: T)(implicit list: List[U]): Option[U] = {
  list.find(_.toString == s.toString)
}

implicit val convert3: Command => String =
  (v: Command) => v.typeName

val res1:String = UpdateMessageCommand
val res: Option[Command] = "add_message1"

我创建了新的转换器convert3，它可以转换Command => String。上面的方法有效，但是我不确定为什么用户为隐式转换覆盖了字符串

  //This is required for implicit conversion.
  override def toString: String = typeName

Answer 1

在帖子中回答：

注意：由于我正在通过转换将两个类型实例转换为字符串来比较它们，因此我必须在Command中重写此用例的toString方法。

因为它是为通用T和U（并且它们没有界限）编写的，所以作者无法调用typeName。

但是老实说，像这样定义一个隐式转换（convert，而不是convert3）并不是一个好主意。

案例对象的scala隐式转换

1 个答案: