WeakObservable

WeakObservable is very similar to Observable from ruby’ standard library, but with the very important difference in that it allows its subscribers to be garbage collected.

First, install the gems with rubygems.

gem install weak_observable

Now include it onto any object, set up your subscribers and play away!

require 'weak_observable'

class Observer
  def update(event, *args, &block)
    puts "[#{event}]: #{args.inspect}"
  end
end

class Playlist
  include WeakObservable::Mixin
end

# Create an observer to wait for notifications.
observer = Observer.new

playlist = Playlist.new
playlist.observers.add(observer)

# Notify all observers. Any arguments and given block goes out to them all.
playlist.observers.notify(:ping)
# ^ the above ends up calling observer.update(:ping)

# Unassign the variable, allowing the observer to be garbage collected.
observer = nil

# Some time passes, ruby garbage collection eventually kicks in, and now…
playlist.observers.notify(:ping) # nothing happens, we have no observers.

There is also the Hub, which is a mix between a WeakObservable and a Hash. You add observers by associating them with a key. A key can have multiple observers. When you notify observers, you supply the key, and observers on that key will be notified, but not any other observers.

require 'weak_observable'

hub = WeakObservable::Hub.new

class Ninja
  def update(event, *args)
    puts "Ninjas: #{event}"
  end
end

class Pirate
  def update(event, *args)
    puts "Pirates: #{event}"
  end
end

ninja_a = Ninja.new
ninja_b = Ninja.new

pirate_a = Pirate.new
pirate_b = Pirate.new

hub.add(Ninja, ninja_a)
hub.add(Ninja, ninja_b)
hub.add(Pirate, pirate_a)
hub.add(Pirate, pirate_b)

hub.notify(Pirate, "Ninjarrrs arrr attacking!")
# ^ notifies all the pirates that ninjas are attacking.

hub.notify(Ninja, "All pirates are down.")
# ^ notifies all ninjas the pirates are all dead.

When all objects of a given key has been garbage collected, that key will also be garbage collected. Because of this property Hubs can be extremely useful interfacing with asynchronous C libraries and their callbacks.

• CRuby 1.9.2, 1.9.3, 2.0.0
• JRuby 1.9-mode
• Rubinius 1.9-mode

I will not be supporting Ruby 1.8.

Please fork the repository and clone it. To get started with development you’ll need to install the development dependencies and make sure you can run the tests. You can easily install all development dependencies using bundler.

$> gem install bundler
$> bundle install # => installs development dependencies

Once you have the dependencies installed you should be able to run the tests.

$> rake

They should be green. Now go ahead and add your tests, add your changes, and push it back up to GitHub. Once you feel you’re done create a pull request. Thank you!

Copyright (c) 2012 Kim Burgestrand

MIT License

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.