So typeclasses in scala are pretty cool...

user-info-extending.scala

case class UserInfo(name: String, email: String)


case class PaidUser(id: Long, name: String, email: String, payments: Double)

object PaidUser {

  class PaidUserExtended(user: PaidUser) {
    def userInfo: UserInfo = UserInfo(user.name, user.email)
  }

  implicit def PaidUser2Extended(user: PaidUser) = new PaidUserExtended(user)

}


case class BasicUser(id: Long, name: String, email: String)

object BasicUser {

  class BasicUserExtended(user: BasicUser) {
    def userInfo: UserInfo = UserInfo(user.name, user.email)
  }

  implicit def BasicUser2Extended(user: BasicUser) = new BasicUserExtended(user)

}


val basic = BasicUser(1, "foo bar", "[email protected]")
val paid = PaidUser(1, "baz bim", "[email protected]", 55.4)

println(basic.userInfo)
// UserInfo(foo bar,[email protected])

println(paid.userInfo)
// UserInfo(baz bim,[email protected])

user-info-typeclass.scala

case class BasicUser(id: Long, name: String, email: String)

case class PaidUser(id: Long, name: String, email: String, payments: Double)


case class UserInfo(name: String, email: String)

object UserInfoMethods {

  trait UserInfoLike[T] {
    def getUserInfo(user: T): UserInfo
  }
  object UserInfoLike {
    // The implicits here can be vals or objects, depending on what you prefer
    implicit val UserInfoLikeBasic = new UserInfoLike[BasicUser] {
      def getUserInfo(user: BasicUser): UserInfo = UserInfo(user.name, user.email)
    }
    implicit object UserInfoLikePaid extends UserInfoLike[PaidUser] {
      def getUserInfo(user: PaidUser): UserInfo = UserInfo(user.name, user.email)
    }
  }

  def userInfo[T](user: T)(implicit tc: UserInfoLike[T]): UserInfo = tc.getUserInfo(user)

}

val basic = BasicUser(1, "foo bar", "[email protected]")
val paid = PaidUser(1, "baz bim", "[email protected]", 55.4)

println(UserInfoMethods.userInfo(basic))
// UserInfo(foo bar,[email protected])

println(UserInfoMethods.userInfo(paid))
// UserInfo(baz bim,[email protected])