Appendix B. OTP Templates
These are the full templates for gen_server, supervisor, and application from the Emacs mode for Erlang. Some pieces are more useful than others, but seeing the full set of expected responses can be useful. (In this context, a template is just a file full of code you can use as a base for creating your own code.)
Note
Remember, the noreply atom doesn’t mean “there will never be a reply” but rather that “this response isn’t a reply.”
Example B-1. A gen_server template from the Erlang mode for Emacs
%%% @author $author%%% @copyright (C) $year, $company%%% @doc%%%%%% @end%%% Created : $fulldate%%%--------------------------------------------------------------------module($basename).-behaviour(gen_server).%% API-export([start_link/0]).%% gen_server callbacks-export([init/1,handle_call/3,handle_cast/2,handle_info/2,terminate/2,code_change/3]).-define(SERVER,?MODULE).-record(state,{}).%%%===================================================================%%% API%%%===================================================================%%--------------------------------------------------------------------%% @doc%% Starts the server%%%% @spec start_link() -> {ok, Pid} | ignore | {error, Error}%% @end%%--------------------------------------------------------------------start_link()->gen_server:start_link({local,?SERVER},?MODULE,[],[]).%%%===================================================================%%% gen_server callbacks%%%===================================================================%%--------------------------------------------------------------------%% @private%% @doc%% Initializes the server%%%% @spec init(Args) -> {ok, State} |%% {ok, State, Timeout} |%% ignore |%% {stop, Reason}%% @end%%--------------------------------------------------------------------init([])->{ok,#state{}}.%%--------------------------------------------------------------------%% @private%% @doc%% Handling call messages%%%% @spec handle_call(Request, From, State) ->%% {reply, Reply, State} |%% {reply, Reply, State, Timeout} |%% {noreply, State} |%% {noreply, State, Timeout} |%% {stop, Reason, Reply, State} |%% {stop, Reason, State}%% @end%%--------------------------------------------------------------------handle_call(_Request,_From,State)->Reply=ok,{reply,Reply,State}.%%--------------------------------------------------------------------%% @private%% @doc%% Handling cast messages%%%% @spec handle_cast(Msg, State) -> {noreply, State} |%% {noreply, State, Timeout} |%% {stop, Reason, State}%% @end%%--------------------------------------------------------------------handle_cast(_Msg,State)->{noreply,State}.%%--------------------------------------------------------------------%% @private%% @doc%% Handling all non call/cast messages%%%% @spec handle_info(Info, State) -> {noreply, State} |%% {noreply, State, Timeout} |%% {stop, Reason, State}%% @end%%--------------------------------------------------------------------handle_info(_Info,State)->{noreply,State}.%%--------------------------------------------------------------------%% @private%% @doc%% This function is called by a gen_server when it is about to%% terminate. It should be the opposite of Module:init/1 and do any%% necessary cleaning up. When it returns, the gen_server terminates%% with Reason. The return value is ignored.%%%% @spec terminate(Reason, State) -> void()%% @end%%--------------------------------------------------------------------terminate(_Reason,_State)->ok.%%--------------------------------------------------------------------%% @private%% @doc%% Convert process state when code is changed%%%% @spec code_change(OldVsn, State, Extra) -> {ok, NewState}%% @end%%--------------------------------------------------------------------code_change(_OldVsn,State,_Extra)->{ok,State}.%%%===================================================================%%% Internal functions%%%===================================================================
Example B-2. A supervisor template from the Erlang mode for Emacs
%%%-------------------------------------------------------------------%%% @author $author%%% @copyright (C) $year, $company%%% @doc%%%%%% @end%%% Created : $fulldate%%%--------------------------------------------------------------------module($basename).-behaviour(supervisor).%% API-export([start_link/0]).%% Supervisor callbacks-export([init/1]).-define(SERVER,?MODULE).%%%===================================================================%%% API functions%%%===================================================================%%--------------------------------------------------------------------%% @doc%% Starts the supervisor%%%% @spec start_link() -> {ok, Pid} | ignore | {error, Error}%% @end%%--------------------------------------------------------------------start_link()->supervisor:start_link({local,?SERVER},?MODULE,[]).%%%===================================================================%%% Supervisor callbacks%%%===================================================================%%--------------------------------------------------------------------%% @private%% @doc%% Whenever a supervisor is started using supervisor:start_link/[2,3],%% this function is called by the new process to find out about%% restart strategy, maximum restart frequency and child%% specifications.%%%% @spec init(Args) -> {ok, {SupFlags, [ChildSpec]}} |%% ignore |%% {error, Reason}%% @end%%--------------------------------------------------------------------init([])->SupFlags=#{strategy=>one_for_one,intensity=>1,period=>5},AChild=#{id=>'AName',start=>{'AModule',start_link,[]},restart=>permanent,shutdown=>5000,type=>worker,modules=>['AModule']},{ok,{SupFlags,[AChild]}}.%%%===================================================================%%% Internal functions%%%===================================================================
Example B-3. An application module template from the Erlang mode for Emacs
%%%-------------------------------------------------------------------%%% @author $author%%% @copyright (C) $year, $company%%% @doc%%%%%% @end%%% Created : $fulldate%%%--------------------------------------------------------------------module($basename).-behaviour(application).%% Application callbacks-export([start/2,stop/1]).%%%===================================================================%%% Application callbacks%%%===================================================================%%--------------------------------------------------------------------%% @private%% @doc%% This function is called whenever an application is started using%% application:start/[1,2], and should start the processes of the%% application. If the application is structured according to the OTP%% design principles as a supervision tree, this means starting the%% top supervisor of the tree.%%%% @spec start(StartType, StartArgs) -> {ok, Pid} |%% {ok, Pid, State} |%% {error, Reason}%% StartType = normal | {takeover, Node} | {failover, Node}%% StartArgs = term()%% @end%%--------------------------------------------------------------------start(_StartType,_StartArgs)->case'TopSupervisor':start_link()of{ok,Pid}->{ok,Pid};Error->Errorend.%%--------------------------------------------------------------------%% @private%% @doc%% This function is called whenever an application has stopped. It%% is intended to be the opposite of Module:start/2 and should do%% any necessary cleaning up. The return value is ignored.%%%% @spec stop(State) -> void()%% @end%%--------------------------------------------------------------------stop(_State)->ok.%%%===================================================================%%% Internal functions%%%===================================================================
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