Later registered events with class method will not be registered on the instance too, because the duplication of events and listeners is being done only when any instance method ( any that use __bus__) is called.

For example, given that dry-monitor registers :sql event with the .register_event(:name):

https://github.com/dry-rb/dry-monitor/blob/7a0625c199c8cbd8d053956b2735d4074a22b0dd/lib/dry/monitor/sql/logger.rb#L5-L10

loading the sql dry-monitor extension after an instance of Publisher was created and consumed will not registers new events if the entire app uses the same instance of 'Publisher' (Dry::Web::Container creates an instance of Notifications publisher that is supposed to be used globally, at least for logging)

Moved from here: dry-rb/dry-monitor#11

Hey guys,

We use dry-monitor together with dry-events in karafka. In order to provide a "safe" API (safe in terms of typo mistakes etc) we've implemented two additional methods for the monitor that could be useful when working with it. Would it fit as a PR in this library?

      # Allows us to subscribe to events with a code that will be yielded upon events
      # @param event_name_or_listener [String, Object] name of the event we want to subscribe to
      #   or a listener if we decide to go with object listener
      def subscribe(event_name_or_listener)
        return super unless event_name_or_listener.is_a?(String)
        return super if available_events.include?(event_name_or_listener)
        raise Errors::UnregisteredMonitorEvent, event_name_or_listener
      end

      # @return [Array<String>] names of available events to which we can subscribe
      def available_events
        __bus__.events.keys
      end

I believe that this behavior would prevent users from subscribing to non-registered events.

Whole monitor can be found here: https://github.com/karafka/karafka/blob/master/lib/karafka/instrumentation/monitor.rb

I would expect calling app.publish('non-existing-event', {}) to fail with a UnknownEvent-like error.

Current behaviour is that you cannot subscribe to a non-existing event (raises Dry::Events::InvalidSubscriberError) but publishing is a no-op.

Since:

In this method, there is simply no listener so the loop is a no-op.

@solnic I have been looking at the code for learning purposes, and notice in the Publisher module, when a new bus is instantiated that name will always be nil

We found (with @mensfeld) that we can notify developers with unused subscriber code. Now we have a question: could it be helpful for community or not?