students.scala

type Email = String

case class User(username: String, givenName: String, familyName: String, email: Email)

sealed abstract class Role(user: User, course: Course)

case class Student(user: User)

case class StudentInCourse(user: User, course: Course) extends Role(user, course)

case class Instructor(user: User, course: Course) extends Role(user, course)

case class Course(
    name: String,
    directory: String,
    instructors: List[Instructor],
    students: List[Student]
)