% version 1
-module(code_change_test).
-behaviour(gen_server).

-export([start/0, stop/0]).
-export([state/0]).

-export([
  init/1,
  handle_call/3, handle_cast/2, handle_info/2,
  terminate/2, code_change/3
]).

start() -> gen_server:start({local, ?MODULE}, ?MODULE, [], []).
stop()  -> gen_server:cast(?MODULE, stop).
state() -> gen_server:call(?MODULE, state).

init(_Args) ->
  {ok, ver1}.

handle_call(state, _From, State) ->
  io:fwrite("State=~p~n", [State]),
  {reply, State, State};
handle_call(_Message, _From, State) ->
  {reply, ok, State}.

handle_cast(stop, State) ->
  {stop, normal, State};
handle_cast(_Message, State) ->
  {noreply, State}.

handle_info(_Info, State) -> {noreply, State}.

terminate(normal, _State) -> ok;
terminate(_, _) -> ok.

code_change(_OldVsn, State, _Extra) ->
  {ok, State}.