From: Robert Klemme <bob.news@...>
Date: 2006-02-02T06:57:17+09:00
Subject: Re: callbacks, events, notification in general

Damphyr wrote:
> ara.t.howard@noaa.gov wrote:
>> On Thu, 2 Feb 2006, Damphyr wrote:
>> 
>>> OK, bare with me, this is brainstorming of a sorts:
>>> I want to have some kind of event notification from my classes.
>>> Typically what I would do would be to pass a logger object and let
>>> the class log by itself, but I'm not really satisfied with this
>>> solution in most cases.
>>> 
>>> What I would prefer was define a callback method and give this to
>>> the object. Then I could do whatever I want with it and not only
>>> use logs. Mostly I want to have progress reports.
>>> 
>>> something like
>>> 
>>> class A
>>>  def set_callback notify
>>>    @notify=notify
>>>  end
>>>  def something
>>>    puts "something"
>>>    send(@notify) if @notify
>>>  end
>>> end
>>> 
>>> def coocoo
>>>     puts "hey"
>>> end
>>> a=A.new
>>> a.something
>>> a.set_callback(:coocoo)
>>> a.something
>>> 
>>> Now this does exactly what I want and can be wrapped up in a module
>>> to be included for general use.
>>> Question: Is there a "better" solution? What are my alternatives?
>>> Cheers,
>>> V.-
>> 
>>     harp:~ > cat a.rb
>>     require "observer"
>> 
>>     class A
>>       include Observable
>>       def something
>>         changed and notify_observers 42
>>       end
>>     end
>> 
>>     class B
>>       def update arg
>>         p arg
>>       end
>>     end
>> 
>>     a = A::new
>>     b = B::new
>> 
>>     a.add_observer b
>>     a.something
>> 
>> 
>>     harp:~ > ruby a.rb
>>     42
>> 
>> always a good start to read about the stdlibs!  ;-)
> Well, actually it would be a good start to remember the names of the
> patterns :) .
> *Then* I can remember that there is an implementation in the standard
> library. I've been staring at the screen for too long I guess.
> There is a slight difference though: In Observer the observer is an
> object that needs to specify the update method.
> I was aiming to provide the notifier with a method, any method, to
> call. Mine is a one-to-one callback between instances.
> With the observer pattern you get one-to-many and the observer can
> observe *any* observable object.
> More generic and at the end more practical because I will end up
> naming everything the same every time I use it.
> Just need to be careful to add one/delete one instead of reassigning
> the callback in order to replace an observer.
> Cheers,

If you want to use another method, you can use a lambda as adapter:

def observe(observable)
  m = lambda {|*a| my_other_method(*a)}
  class <<m
    alias update call
  end
  observable.add_observer m
end

Kind regards

    robert