class UserService  :5-28
  function getUser(string $id) → ?User  :14-14
  function createUser(array $data) → User  :19-19
  function validateUser(User $user) → bool  :24-24
interface Repository  :30-34
  function findById(string $id) → mixed  :32-32
  function save(mixed $entity) → mixed  :33-33
function hashPassword(string $password) → string  :36-39
