def roles(*roles) 
      self.valid_roles = Array[*roles].flatten.map { |r| r.to_sym }
    end
def roles(*roles) 
      self.valid_roles = Array[*roles].flatten.map { |r| r.to_sym }
    end
:call-seq:
   roles(:role_1, ..., :role_n)
   roles('role_1', ..., 'role_n')
   roles([:role_1, ..., :role_n])
   roles(['role_1', ..., 'role_n'])

 declare valid roles