Eventful¶ ↑

Eventful is a small extension on top of Ruby’s Observable module that implements named events, block listeners and event bubbling. It allows much more flexible event handling behaviour than is typically allowed by Observable, which requires listeners to be objects that implement update and provides no simple way of calling subsets of observers based on event type.

Make a class listenable by mixing Eventful into it:

class Watcher
  include Eventful
end

Register event listeners using on with an event name and a block. Publish events using fire with the event name. The block accepts the object that published the event, along with any parameters passed to fire.

w = Watcher.new

w.on(:filechange) { |watcher, path| puts path }
w.on(:filedelete) { |watcher, path| puts "#{ watcher } deleted #{ path }" }

w.fire(:filechange, '/path/to/file.txt')
w.fire(:filedelete, '/tmp/pids/event.pid')

# prints...
# /path/to/file.txt
# #<Watcher:0xb7b485a4> deleted /tmp/pids/event.pid

The on method returns the Observer object used to represent the listener, so you can remove it using delete_observer.

obs = w.on(:filechange) { |watcher| ... }

# listener will not fire after this
w.delete_observer(obs)

Instead of passing a block, you can add behaviour to objects by chaining method calls after the on call. For example:

class Logger
  include Eventful

  def print(message)
    puts message
  end
end

log = Logger.new
log.on(:receive).print "Received message"

# Calls `log.print "Received message"`
log.fire(:receive)

When you fire an event, the event ‘bubbles’ up the type system. What this means is that you can listen to events on all the instances of a class just by placing an event listener on the class itself. As above, the listener is called with the instance that fired the event.

Logger.on(:receive) { |log, msg| puts "#{ log } :: #{ msg }" }

l1, l2 = Logger.new, Logger.new

l1.fire(:receive, 'The first message')
l2.fire(:receive, 'Another event')

# prints...
# #<Logger:0xb7bf103c> :: The first message
# #<Logger:0xb7bf1028> :: Another event

Method chains can also be used, and they will be replayed on the instance that initiated the event.

# Calls `log.print "Received message"`

Logger.on(:receive).print "Received message"

log = Logger.new
log.fire(:receive)

(The MIT License)

Copyright © 2009-2012 James Coglan

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