From: Eric Hodel <drbrain@...7.net>
Date: 2006-03-21T16:35:33+09:00
Subject: Re: A long call chain...

On Mar 20, 2006, at 10:48 PM, Benjohn Barnes wrote:

> Hello everyone. I'm hoping to do something like this (and then  
> automate it up by putting something neat in to a mix in module)...
>
> class Test
> def xxx; [1]; end
> alias xxx_old xxx
> def xxx; xxx_old + [2]; end
> alias xxx_old xxx
> def xxx; xxx_old + [3]; end
> alias xxx_old xxx
> ...
> end

Yuck.

> In real use, these various defs and aliases would be in different  
> files, but would often be putting things in to the same class. The  
> above doesn't work - I think it's leading to a non terminating  
> recursive function.
>
> My first question is, "is it correct that this doesn't work?"

The fact that this is unmaintainably difficult to do is a very, very  
big clue.  Note also that this will break if you change the order of  
require, not good.

> I'd like to use a mechanism like this to enable me to have a kind  
> of hookable function in a class. As I said, the alias process would  
> be encapsulated by waving my hands and working that out later, but  
> probably making use of method_defined.
>
> The mechanism allows you to build up an event handler: you send an  
> event to a class instance, and any receivers that are registered  
> for that event (by having defined the method to pick it up) will  
> get it. Example hookable methods for my system will be:  
> is_being_setup, will_be_torn_down, has_recieved_message  
> will_send_message.

observer.rb provides something similar to what you want, event  
notification.

> It's worth noting that the will_be methods should probably be  
> executed in the reverse order from that in which they are defined!
>
>  I'm pretty sure this is a good plan, but...
>
> Question: "Does this seem like a good plan?"

Not with random aliasing it doesn't.

> Finally, as this doesn't work, can you see a nicer way to implement  
> it? I think I could capture the function each time it gets defined,  
> and put it in to class state, but it would need to be per class, I  
> think, rather than just on in the base class. I've thought about  
> several variations, but none of them seem to be very nice at all.

Check out MuffDaddy:

http://blog.zenspider.com/archives/2005/02/muffdaddy_the_u.html

What do you want to use this for?  Why?

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

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