案例类上的Scala Type Erasure如何解决

Question

我有一个 trait 和两个扩展它的 case 类：

trait Authenticatable {
  val email: String
  val pass: String
  val id: Long
  val sessionid: String
}

case class Admin(
  id: Long,
  email: String,
  pass: String,
  sessionid: Option[String] = None) extends Authenticatable

case class Client(
  id: Long,
  email: String,
  pass: String,
  sessionid: Option[String] = None) extends Authenticatable

我有一些函数应该验证用户，用新的 sessionid 复制对象并返回它。

  def auth(email: String, password: String): Try[Admin] ={
    checkPass(models.Admin.findBy(sqls"email = $email"), password)
  }

  def auth(email: String, password: String, customer: Customer): Try[Customer] ={
    checkPass(models.Customer.findBy(sqls"email = $email"), password)
  }

  private def checkPass (model: Option[Authenticatable], password: String): Try[Authenticatable]={
    model match {
      case Some(m) => check(password, m.pass).map(_ => m)
      case _ => Failure(new Exception("Authentication failure!"))
    }
  }

问题是：我无法在 auth 函数中复制对象，因为函数 checkPass 返回 Authenticatable 而不是 Client 或 Admin 类，并且 Authenticatable 没有案例类的复制方法。

解决这个问题的正确方法是什么？

Answer 1

如果您使用类型参数，您可以避免丢弃checkPass 将始终返回与提供给它的Authenticable 相同类型的信息：

private def checkPass[A <: Authenticatable](model: Option[A], password: String): Try[A] =
  // exactly the same body here

这意味着在auth 你可以有例如：

def auth(email: String, password: String): Try[Admin] =
  checkPass(models.Admin.findBy(sqls"email = $email"), password)
    .map(_.copy(sessionid = Some("whatever")))

Answer 2

我建议向Authenticable 添加一个抽象方法，该方法设置会话ID，并通过使用生成的copy 方法由各个案例类实现。

trait Authenticable {
  def email: String
  def pass: String
  def id: Long
  def sessionid: Option[String]
  def setSessionId(id: String): Authenticable
}

case class Admin(
  id: Long,
  email: String,
  pass: String,
  sessionid: Option[String] = None) extends Authenticable {
  def setSessionId(id: String) = copy(sessionid = Some(id))
}

case class Client(
  id: Long,
  email: String,
  pass: String,
  sessionid: Option[String] = None) extends Authenticable {
  def setSessionId(id: String) = copy(sessionid = Some(id))
}