User-Defined Behaviours

To implement a user-defined behaviour, write code similar to code for a special process but calling functions in a callback module for handling specific tasks.

If it is desired that the compiler should warn for missing callback functions, as it does for the OTP behaviours, implement and export the function:

behaviour_info(callbacks) ->
    [{Name1,Arity1},...,{NameN,ArityN}].

where each {Name,Arity} specifies the name and arity of a callback function.

When the compiler encounters the module attribute -behaviour(Behaviour). in a module Mod, it will call Behaviour:behaviour_info(callbacks) and compare the result with the set of functions actually exported from Mod, and issue a warning if any callback function is missing.

Example:

%% User-defined behaviour module
-module(simple_server).
-export([start_link/2,...]).
-export([behaviour_info/1]).

behaviour_info(callbacks) ->
    [{init,1},
     {handle_req,1},
     {terminate,0}].

start_link(Name, Module) ->
    proc_lib:start_link(?MODULE, init, [self(), Name, Module]).

init(Parent, Name, Module) ->
    register(Name, self()),
    ...,
    Dbg = sys:debug_options([]),
    proc_lib:init_ack(Parent, {ok, self()}),
    loop(Parent, Module, Deb, ...).

...

In a callback module:

-module(db).
-behaviour(simple_server).

-export([init/0, handle_req/1, terminate/0]).

...