From: Damphyr <damphyr@...>
Date: 2006-02-02T01:45:37+09:00
Subject: Re: callbacks, events, notification in general

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,
V.-
-- 
http://www.braveworld.net/riva

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