case class User  :4-9
  def findById(id) → Option[T]  :7-7
  def save(entity) → T  :8-8
class UserService  :11-18
  def getUser(id) → Option[User]  :12-12
  def createUser(dto) → User  :14-14
object UserService  :20-22
  def apply(repo) → UserService  :21-21
def hashPassword(password) → String  :24-24
