ObjectPubSub

ObjectPubSub is an implementation of the Observer pattern for Ruby that provides finer-grained controll over message passing than does the Observable module from Ruby's stdlib. The including class can publish multiple event types, and the subscribers can specify both which event types to listen for and what method on the subscriber should be invoked for each event type.

Installation

Add this line to your application's Gemfile:

gem 'object_pub_sub'

And then execute:

$ bundle

Or install it yourself as:

$ gem install object_pub_sub

Usage

In the class that will be publishing events (the "Observable"), simply include ObjectPubSub and then publish events where appropriate:

class UserValidator
  include ObjectPubSub

  attr_reader :user, :errors

  def initialize(user)
    @user = user
    @errors = {}
  end

  def validate
    validate_username #def exluded for brevity
    validate_password #def exluded for brevity
    validate_email #def exluded for brevity

    notify_subscribers
  end

  private

  def notify_subscribers
    if errors.any?
      publish_event(:invalid, errors)
    else
      publish_event(:valid, user)
    end
  end
end

Then, objects that care about those events can subscribe to them:

class ValidationLogger
  def initialize(name, logger = nil)
    @logger = logger || Logger.new(STDERR)
    @name = name
  end

  def log_validation_error(errors)
    logger.warn("Validation errors on #{name}: #{errors}")
  end
end

class CreateUser
  def initialize(logger = nil)
    @logger = logger
  end

  def perform(user_attrs)
    user = User.new(attrs)
    validation_logger = ValidationLogger.new("User creation", logger)
    validator = UserValidator.new(user)
    validator.add_subscriber(self, :valid => :handle_valid_user, :invalid => :handle_invalid_user)
    validator.add_subscriber(validation_logger, :invalid => :log_validation_error)
    validator.validate
  end

  def handle_valid_user(user)
    # ...
  end

  def handle_invalid_user(errors)
   # ...
  end
end

CreateUser.new \
  .perform(:username => 'foo', :email => 'foo@example.com', :password => 'foopassword')

See the examples under /spec for more information.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request