Circulate

This gem lets you circulate messages around the ActiveSupport::Notifications pubsub system. It provides a syntax for publishing calls to instance methods and subscribing to them through class methods.

gem install circulate

The gem relies on active_support, but not the entire Rails stack. It also requires Ruby 2.0.0-p195+. Note that Ruby 2.0.0-p0 will not work because of a bug in Module.prepend.

class ChicagoTribune
    include Circulate::Publisher

    publish :daily_edition

    def daily_edition
        puts "delivered to your door!"
    end
end

class Reader
    include Circulate::Subscriber

    subscribe :daily_edition

    def self.daily_edition(tribune)
        puts "Tribune edition #{tribune} received!"
    end
end

tribune = ChicagoTribune.new
tribune.daily_edition

Outputs...

delivered to your door!
Tribune edition #<ChicagoTribune:0x007fd78350d1d0> received!

So classes can be "poked" when a method is called on an instance. Sometimes you don't want or need to have an instance object sitting around waiting for a notification. Also, it removes you from having to keep track of notifications by String name, and you don't have to deal with the somewhat cumbersome ActiveSupport::Notifications syntax.

The gem also includes RSpec matchers for your test suite. To use them add require 'circulate/matchers' to your spec_helper. Then, in your tests, you can:

describe ChicagoTribune do
    it { should publish :daily_edition }
end

describe Reader do
    it { should subscribe_to :daily_edition }
end