anchor.diff:  -spec(get() -> {ok, [Rec :: #device{}]} | {error, string()}).
   get() ->
     gen_server:call(?SERVER, {get}).
  +
  +-spec(create(Device :: #device{}) -> {ok, #device{}} | {error, string()}).
  +create(Device) ->
  +  gen_server:call(?SERVER, {create, Device}).
   
   %%--------------------------------------------------------------------
   %% @doc
  
positive.code: %%%===================================================================
  
  do_get_devices(State = #state{cache = Cache}) ->
    {reply, {ok, ets:tab2list(Cache)}, State}.
negative.code:   {stop, Reason :: term(), NewState :: #state{}}).
  handle_call({get}, _From, State) ->
    do_get_devices(State);
  handle_call({create, User}, _From, State) ->
    do_create_device(State, User);
  handle_call(_Request, _From, State) ->
    {reply, ok, State}.
  
  