Scala 更好的案例类继承弃用解决方案？

我正在使用公认的有点陈旧的Scala编程[Subramaniam，2009]，在使用下面的case类进行第9.7节匹配时遇到了一个令人不安的编译器警告

下面是我根据对错误消息的解释设计的解决方案。我怎样才能使用更接近本书示例初衷的解决方案来改进这段代码？特别是如果我想使用密封的案例类功能

/** 
 * [warn] case class `class Sell' has case ancestor `class Trade'.  
 * Case-to-case inheritance has potentially dangerous bugs which 
 * are unlikely to be fixed.  You are strongly encouraged to instead use 
 * extractors to pattern match on non-leaf nodes.
 */

// abstract case class Trade()
// case class Buy(symbol: String, qty: Int) extends Trade
// case class Sell(symbol: String, qty: Int) extends Trade
// case class Hedge(symbol: String, qty: Int) extends Trade

object Side extends Enumeration {
  val BUY = Value("Buy")
  val SELL = Value("Sell")
  val HEDGE = Value("Hedge")
}

case class Trade(side: Side.Value, symbol: String, qty: Int)

def process(trade: Trade) :String = trade match {
  case Trade(_, _, qty) if qty >= 10000 => "Large transaction! " + trade
  case Trade(_, _, qty) if qty % 100 != 0 => "Odd lot transaction! " + trade 
  case _ => "Standard transaction: " + trade
}

---

而不是从封闭的特质交易中继承

sealed trait Trade
case class Buy(symbol: String, qty: Int) extends Trade
case class Sell(symbol: String, qty: Int) extends Trade
case class Hedge(symbol: String, qty: Int) extends Trade

---

而不是从封闭的特质交易中继承

sealed trait Trade
case class Buy(symbol: String, qty: Int) extends Trade
case class Sell(symbol: String, qty: Int) extends Trade
case class Hedge(symbol: String, qty: Int) extends Trade

---

嗯……好像有几本书的标题是《Scala编程》。参考SubramaniamAnd的一本，然后是Scala编程，Odersky的经典之作。嗯……似乎有几本书的标题是Scala编程。参考SubramaniamAnd的一个，然后是Scala编程，Odersky的经典。