From: Joel VanderWerf <vjoel@...>
Date: 2002-11-11T11:21:46+09:00
Subject: [ANN] observable


Hello, "observable.rb" is a variation on the observer pattern. It allows 
multiple observers to register interest in the value of a variable, and 
be notified when it changes. The main differences with Observer 
(observer.rb) are that it is per-variable, not per-object, that it is 
based on closures, and that variable state can be matched against 
several patterns or values, each with a corresponding action.

Source, examples, and docs are at:

   http://redshift.sourceforge.net/observable/

A simple example:

     class Window
       observable :visible # true or false
     end

     class WindowVisibleMenuCmd
       def initialize window
         window.when_visible true do
           @checked = true
         end
         window.when_visible false do
           @checked = false
         end
         @window = window
       end

       def do_command
         @window.visible = !@checked
       end

       def inspect
         "menu is #{"not " if not @checked}checked" +
         " and window is #{"not " if not @window.visible}visible"
       end
     end

     window = Window.new
     window.visible = true

     menu_cmd = WindowVisibleMenuCmd.new window

     puts "Before command, " + menu_cmd.inspect
     menu_cmd.do_command
     puts "After command, " + menu_cmd.inspect

     # Output:
     # Before command, menu is checked and window is visible
     # After command, menu is not checked and window is not visible