From: Robert Klemme <bob.news@...>
Date: 2005-10-07T23:46:50+09:00
Subject: Re: Event Handling

James Edward Gray II wrote:
> On Oct 7, 2005, at 8:46 AM, iamscottwalter@gmail.com wrote:
>
>> Hi,
>
> Hello and welcome.
>
>> I am coming from the Java world and was wondering if there ins
>> anything
>> in Ruby similar to Java's event processing?  For  example I have a
>> particular Object that can fire off an event to all objects that
>> listen
>> for that event.  A more real world example would be that I have a
>> delete() method that was called and I want to let all interested
>> parties know that the delete() method was called.
>>
>> In the Java space I would setup an event listener.  When the delete()
>> method would be called I wouold send an event to all my registered
>> listeners.
>
> I think you are looking for observer, in Ruby's standard library:
>
> http://www.ruby-doc.org/stdlib/libdoc/observer/rdoc/index.html

This started in interesting thought with me: a block would come in handy
as listener as well.  In fact "adapter" might be a better name and what we
get then seems to be quite similar to the C# approach.

class SomeObserver
  def register(observable)
    observable.add_observer do |*a|
      puts "changed" if DEBUG
      @model_change = true
      # ...
    end
  end
end

Disadvantages I see so far

 - removal of adapters is impossible

 - a lot unnecessary adapter objects might be created

Alternative approach:

class SomeObserver
  def register(observable)
    observable.add_observer adapter(observable) do |*a|
      puts "changed" if DEBUG
      @model_change = true
      # ...
    end
  end

  def adapter(obj,&b)
    @adapters[obj] ||= ( b; class <<b; alias :update :call; end; b )
  end
end

Sorry, just loud thinking...

Kind regards

    robert