I'm writing an event manager that will take a lot of different event handlers. This event manager will be notified with a lot of different events. Each handler only handle certain events, and ignore the rest. Each handler can also trigger certain other events based on situation.
For example, first handler to handle Event1
-module (first_handler).
-behavior (gen_event).
...
handle_event(Event1, State) -> {ok, State};
handle_event(_, State) -> {ok, State}.
Second handler to handle Event2
-module (second_handler).
-behavior (gen_event).
...
handle_event(Event2, State) ->
gen_event:notify(self(), Event1),
{ok, State};
handle_event(_, State) -> {ok, State}.
The event triggering can be done by calling gen_event:notify(self(), NewEvent) within a handle_event of the handler, but I would rather abstract and export that out so that it can be called from the event manager.
Since pattern matching and ignoring events and triggering events are common to all the handlers, is there anyway I can extend gen_event behavior to provide those as built-ins?
I'll start with the default way to create a custom behavior:
-module (gen_new_event).
-behaviour (gen_event).
behaviour_info(Type) -> gen_event:behaviour_info(Type).
I'm not sure what to do next.
Your installed handlers are already running in the context of the event manager which you start and then install handlers into. So if their handle-event function throws out data, they already do what you want.
You don't need to extend the event behaviour. What you do is:
handle_event(Event, State) ->
generic:handle_event(Event, State).
and then let the generic module handle the generic parts. Note that you could supply generic a way to callback to this handler module for specialized handler behaviour should you need it. For example:
generic:handle_event(fun ?MODULE:callback/2, Event, State)...
and so on.