Equivalent of Django Signals for Rails?

Question

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.

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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.

Answer 1

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.

Answer 2

What about the 'wisper' gem? https://github.com/krisleech/wisper

Wisper is a Ruby library for decoupling and managing the dependencies of your Ruby objects using Pub/Sub.

It is commonly used as an alternative to ActiveRecord callbacks and Observers to reduce coupling between data and domain layers.

Answer 3

Perhaps acts_as_state machine will help. Most of this functionality has recently been baked into Rails edge.

Answer 4

I just implemented a gem with that. https://github.com/pkoch/django_signal/

Answer 5

Ruby gem 'watchable' is the most appropriate choice https://github.com/jbarnette/watchable

It has a syntax that is very familiar to Django's (and other frameworks, like Qt and many others).