anchor.diff:  -export([
     get/0,
     create/1,
  -  update/1
  +  update/1,
  +  delete/1
   ]).
   
   %% gen_server callbacks
  
positive.code:   do_create_device(State, Device);
  handle_call({update, Device}, _From, State) ->
    do_update_device(State, Device);
  handle_call(_Request, _From, State) ->
    {reply, ok, State}.
  
  
negative.code: -spec(update(Device :: #device{}) -> {ok, #device{}} | {error, string()}).
  update(Device) ->
    gen_server:call(?SERVER, {update, Device}).
  
  -spec(delete(Device :: #device{}) -> {ok, #device{}} | {error, string()}).
  delete(Device) ->
    gen_server:call(?SERVER, {delete, Device}).
  
  %%--------------------------------------------------------------------
  %% @doc
  