= announcements

http://www.bofh.org.uk/articles/tag/announcementsproject

== DESCRIPTION:

A port of Vassily Bykov's Smalltalk Announcements framework. Think of it as Observer/Observable on steroids.

== FEATURES/PROBLEMS:

=== Problems first

This is very much a first cut. Testing is sparse because this is mostly a direct port from a Smalltalk package that's pretty much test free. The API also a pretty much straight port of the Smalltalk and isn't what could be called idiomatic Ruby just yet.

=== Features

• Announcements are objects and can carry all the information a subscriber will need.
• Small, uniform interface for subscription

== SYNOPSIS:

class ObservableValue include Announcements class ChangeAnnouncement < Announcements::Anouncement attr_accessor :from, :to

  def initialize(from, to)
    @from, @to = from, to
  end

  def inspect
    self.class.to_s.gsub(/([a-z])(A-Z)/) { $1 + ' ' + $2}.downcase << 
      " from #{@from.inspect} to #{@to.inspect}"
  end
end

class ValueWillChange <  ChangeAnnouncement
  def veto!
    @vetoed = true
  end

  def vetoed?
    @vetoed
  end
end

class ValueChanging < ChangeAnnouncement; end
class ValueChanged < ChangeAnnouncement; end

def self.announcer
  @@announcer ||= Announcements::Announcer.new
end

def announce(*args)
  self.class.announcer.announce(*args)
end

def value=(new_value) 
  unless announce(ValueWillChange.new(@value, new_value)).vetoed?
    announce(ValueChanging.new(@value, new_value)
    change_complete = ValueChanged.new(@value, new_value)
    @value = new_value
    announce(change_complete)
end

end

Spy on all the changes

ObservableValue.watch(ObservableValue::ChangeAnnouncement) do |notice, sender| puts "#{announcer.inspect} #{announcement.inspect}" end

Remember changes for undoing

ObservableValue.watch(ObservableValue::ValueChanged) do |notice, sender| command_history << UndoableCommand.new(sender, notice.from, notice.to) end

== REQUIREMENTS:

• Rspec, but only if you want to run the tests
• Er...
• That's it

== INSTALL:

sudo gem install announcements

== COPYRIGHT:

Copyright (c) 2008 Piers Cawley

This library is free software; you can redistribute it and/or modify it under the same terms as Ruby itself.

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.