Scala中基于列表中的固定元素的动态大小写匹配

Question

假设我有一个可能的列表信用卡

val availableCreditsCard = List(MasterCardCreditCard, VisaCreditCard)

这两个类都扩展了一个名为CreditCard的特征

现在，我想创建一个名为 isValid 的方法，它接受 trait CreditCard

类似：

  def isValid(creditCard: CreditCard): Boolean = {
    creditCard match {
      case t: MasterCardCreditCard => MasterCardCreditCardPayment.isValid(t)
      case s: VisaCreditCard => VisaCreditCardPayment.isValid(s)
    }
  }

MasterCardCreditCardPayment 和 VisaCreditCardPayment 都扩展了一个名为 CreditCardPayment 的特征。

所以，现在，我的问题是，如果我想用他自己的 CreditCardPayment (AmexCreditCardPayment) 添加一个新的可能的 CreditCard (Amex)，但只需更改列表 availableCreditsCard 并且不触及 在 isValid 方法中匹配/大小写？

是否可以根据availableCreditsCard 列表动态创建此匹配/案例？

编辑

这是 CreditCardPayment 特征。

trait CreditCardPayment[CreditCard] {
  def isValid(creditCard: CreditCard): Boolean
  def checkCVV(creditCard: CreditCard): Boolean
}

还有一个VisaCreditCardPayment的例子

object VisaCreditCardPayment extends CreditCardPayment[VisaCreditCard] {

  override def isValid(creditCard: VisaCreditCard): Boolean = {
    val listValidCreditCard = loadFile()
    listValidCreditCard.contains(creditCard)
  }

  //Implemented because it the trait, not necessary
  override def checkCVV(creditCard: VisaCreditCard): Boolean = {
    val listCreditCard = loadFile()
    val cvvToCheck = creditCard.cvv
    listCreditCard.exists(_.cvv == cvvToCheck)
  }
}

现在，您的建议是，在 isValid 方法中，使用 case t => CreditCardPayment.isValid(t)。这甚至是不可能的，因为CreditCardPayment 是一个特征:(

Answer 1

如果您希望它“动态”，只需使用继承而不是“侧面”实现它：

   sealed trait CreditCard {
      def isValid: Boolean
   }

   class MasterCard extends CreditCard {
      def isValid = MasterCardCreditCardPayment.isValid(this)
   }
   class Visa extends CreditCard {
      def isValid = VisaCreditCardPayment.isValid(this)
   }

现在，您只需执行def isValid(c: CreditCard) = c.isValid，无需任何match 语句保持同步。

当你添加美国运通时：

   class Amex extends CreditCard {
       def isValid = AmexCreditCardPayment.isValid(this)
   }

isValid(amex) 可以正常工作，无需更新。

Answer 2

补充 Dima 的回答。因为，您总是希望将isValid 逻辑委托给适当的Payment。我将向您介绍两种不重新定义每个子类中的方法的方法。

一种使用 F-Bounded Polymorphism 的方法，每个子类都需要相当多的样板代码，而且它不是完全类型安全 - 因此可能不值得工作。
第二个使用 typeclasses，这将更加typesafe，并且每张新卡所需的样板文件更少。
有关 F-Bounded 与 Typeclasses 的更详细讨论，请阅读 this 文章。

使用 F-Bounded

sealed trait CreditCardPayment[CC <: CreditCard[CC]] {
  def isValid(creditCard: CC): Boolean
  def checkCVV(creditCard: CC): Boolean
}

object VisaCreditCardPayment extends CreditCardPayment[VisaCreditCard] {
  private final val validCreditCards: List[VisaCreditCard] = ???

  override def isValid(creditCard: VisaCreditCard): Boolean =
    validCreditCards.contains(creditCard)

  override def checkCVV(creditCard: VisaCreditCard): Boolean =
    validCreditCards.exists(_.cvv == creditCard.cvv)
}

object MasterCreditCardPayment extends CreditCardPayment[MasterCreditCard] {
  private final val validCreditCards: List[MasterCreditCard] = ???

  override def isValid(creditCard: MasterCreditCard): Boolean =
    validCreditCards.contains(creditCard)

  override def checkCVV(creditCard: MasterCreditCard): Boolean =
    validCreditCards.exists(_.cvv == creditCard.cvv)
}

sealed trait CreditCard[CC <: CreditCard[CC]] { self: CC =>
  def paymentMethod: CreditCardPayment[CC]

  def cvv: String

  final def isValid: Boolean =
    paymentMethod.isValid(this)
}

final class VisaCreditCard (override val cvv: String) extends CreditCard[VisaCreditCard] {
  override final val paymentMethod: CreditCardPayment[VisaCreditCard] = VisaCreditCardPayment
}

final class MasterCreditCard (override val cvv: String) extends CreditCard[MasterCreditCard] {
  override final val paymentMethod: CreditCardPayment[MasterCreditCard] = MasterCreditCardPayment
}

使用类型类

sealed trait CreditCardPayment[CC <: CreditCard] {
  def isValid(creditCard: CC): Boolean
  def checkCVV(creditCard: CC): Boolean
}

sealed trait CreditCard {
  def cvv: String
}

// Provides the 'isValid' & 'checkCVV' extension methods to any CredictCard.
implicit class CreditCardOps[CC <: CreditCard](val self: CC) extends AnyVal {
  def isValid(implicit payment: CreditCardPayment[CC]): Boolean =
    payment.isValid(self)

  def checkCVV(implicit payment: CreditCardPayment[CC]): Boolean =
    payment.checkCVV(self)
}

final class VisaCreditCard (override val cvv: String) extends CreditCard

object VisaCreditCard {
    final implicit val VisaCreditCardPayment: CreditCardPayment[VisaCreditCard] = new CreditCardPayment[VisaCreditCard] {
      final val validCreditCards: List[VisaCreditCard] = ???

      override def isValid(creditCard: VisaCreditCard): Boolean =
        validCreditCards.contains(creditCard)

      override def checkCVV(creditCard: VisaCreditCard): Boolean =
        validCreditCards.exists(_.cvv == creditCard.cvv)
    }
}

final class MasterCreditCard (override val cvv: String) extends CreditCard

object MasterCreditCard {
  final implicit val MasterCreditCardPayment: CreditCardPayment[MasterCreditCard] = new CreditCardPayment[MasterCreditCard] {
    final val validCreditCards: List[MasterCreditCard] = ???

    override def isValid(creditCard: MasterCreditCard): Boolean =
      validCreditCards.contains(creditCard)

    override def checkCVV(creditCard: MasterCreditCard): Boolean =
      validCreditCards.exists(_.cvv == creditCard.cvv)
  }
}

使用 typeclass 方法，您还可以将 CreditCards 的 isValid 方法定义为一个函数。
（这样您就不需要定义和导入CreditCardOps隐式/值类）.

def isValid[CC <: CreditCard](cc: CC)(implicit payment: CreditCardPayment[CC]): Boolean =
  payment.isValid(cc)