Boilerplate gen_server

example_server.erl

-module(example_server).
-export([start_link/0, start/0]).
-behaviour(gen_server).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

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

init([]) ->
    State = undefined,
    {ok, State}.

handle_call(_Req, _From, State) ->
    {reply, ok, State}.

handle_cast(_Req, State) ->
    {noreply, State}.

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

terminate(_Reason, _State) ->
    ok.

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