In Rails, the closest I’ve seen to Django Signals are Observers. The problem with them is that they’re restricted to triggering callbacks on hardcoded events related to a model’s lifecycle.
Django signals can be created anywhere, triggered anywhere and handled anywhere. The model lifecycle callbacks are just regular signals that happen to come built-in and that are triggered by the ORM.
Does anyone know of a similarly general solution for Rails? It could be some generic Ruby library, not tied to Rails, which would be even better.
Edit: Observer is the closest thing, but it’s not what I’m looking for. It’s a one-to-many solution. Anyone can listen, but only the originating object can post. I’d like something where you declare a signal, and anyone can trigger it as well as handle it. Also, I don’t like the fact that the Ruby Observer dictates that the handler have an #update method. I’d like to be able to pass any method reference with the appropriate signature.
I could use the Ruby Observer to implement my own such broker, but I’m trying to learn if someone already did it.
I think a closer equivalent than Rails’ Observer is the standard Ruby Observable module. It lets you add a list of observers to an object and the object can then send notifications to the observers when it changes.