Watchable

A simple event/notification mixin, reluctantly extracted to a gem. This is code I've had floating around for a few years now, but I've also incorporated a few extras from node.js' EventEmitter, jQuery, and Backbone.Events.

Examples

Fixtures

require "watchable"

class Frob
  include Watchable
end

class Callable
  def call *args
    p :called! => args
  end
end

Watching and Firing

Events can have any number of watchers. Each watcher will be called in order, and any args provided when the event is fired will be passed along. Watchers will most commonly be blocks, but any object that responds to call can be used instead.

frob = Frob.new

frob.on :twiddle do |name|
  puts "#{name} twiddled the frob!"
end

frob.on :twiddle do |name|
  puts "(not that there's anything wrong with that)"
end

frob.on :twiddle, Callable.new
frob.fire :twiddle, "John"

Result

John twiddled the frob!
(not that there's anything wrong with that)
{ :called! => ["John"] }

Watching Everything

Want to see every event? Register for :all. The first argument will be the name of the fired event.

frob = Frob.new

frob.on :all do |event, culprit|
  p :fired => [event, culprit]
end

frob.fire :foo, "John"

Result

{:fired => [:foo, "John"]}

Watching Once

Only want to be notified the first time something happens? once is like on, but fickle.

frob = Frob.new

frob.once :twiddle do
  p :twiddled!
end

frob.fire :twiddle
frob.fire :twiddle

Result

:twiddled!

Unwatching

Specific blocks or callable objects can be removed from an event's watchers, or all the event's watchers can be removed.

b    = lambda {}
frob = Frob.new

frob.on :twiddle, &b

frob.off :twiddle, b  # removes the 'b' watcher, same as frob.off :twiddle, &b
frob.off :twiddle     # removes all watchers for the 'twiddle' event

Compatibility

Watchable is actively developed against MRI Ruby 1.8.7 as a least common denominator, but is widely tested against other Ruby versions and implementations. Check the travis-ci page for details.

License (MIT)

Copyright 2012 John Barnette (john@jbarnette.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.