case class StudentImpl(override val name: String, override val year: Int) extends Student {

  override def enrolling(courses: Course*): Unit = courses foreach enrolling(_)

  private def enrolling(course: Course): Unit = {coursesList = List.append(coursesList, List.Cons(course, List.Nil()))}

  override def hasTeacher(teacher: String): Boolean = List.contains(List.map(coursesList)(c => c.teacher))(teacher)

  private var coursesList: List[Course] = List.Nil()

  override def courses: List[String] = List.map(coursesList)(c => c.name)
}