observable_with_blocks.rb

# Make up for Ruby's odd lack of support for blocks as observers
# 
#   class Foo
#     include Observable::Blocks
#   end
#   
#   f = Foo.new
#   f.add_observer { puts "f changed" }

require 'observer'

module Observable
  module Blocks
    include Observable
    
    class Observer
      def initialize(&block)
        @block = block
      end
      
      def update(*args)
        @block.call(*args)
      end
    end
    
    def add_observer(*args, &block)
      if block_given?
        args[0] = Observer.new(&block)
        args[1] = :update if args[1]
      end
      super(*args)
    end
    
    # Ojay-style message passing
    def on(message, &block)
      add_observer do |*args|
        block.call *([self] + args[1..-1]) if args.first == message
      end
    end
    
  end
end