Scala: Copying case classes with trait

Question

I'm fairly new to Scala and I have a question about the best way to copy a case class while preserving data that comes from traits. For example, let's say I have the following:

trait Auditing {

  var createTime: Timestamp = new Timestamp(System.currentTimeMillis)
}

case class User(val userName: String, val email: String) extends Auditing

val user = User("Joe", "[email protected]")

Then I want to make a new copy with one parameter changed:

val user2 = user.copy(email = "[email protected]")

Now, in the example above, the property createTime does not get copied over because it is not defined in the constructor of the User case class. So my question is: assuming that moving createTime into the constructor is not an option, what is the best way for getting a copy of the User object that includes the value from the trait?

I'm using Scala 2.9.1

Thanks in advance! Joe

Answer 1

You can override the copy method with that behavior.

case class User(val userName: String, val email: String) extends Auditing
{
  def copy(userName = this.userName, email = this.email) {
   val copiedUser = User(userName, email)
   copiedUser.createTime = createTime
   copiedUser      
  }
}