From: Yves Vandriessche
Subject: change-class with non-standard-class metaclasses
Date: Thu, 06 Jul 2006 17:00:20 +0000
Message-ID: <e8jfj4$7s5$1@ikaria.belnet.be>

Say I want to convert a simple rectangle class to a different one, such 
as the gdk:rectangle class to be used in a wrapper.

(change-class my-rectangle 'gdk:rectangle)

The problem here is that the gdk wrapper library specifies its own 
meta-class for gdk:rectangle, instead of using standard-class.  This 
means that the method selection for change-class fails.

How could I work around this problem?  I'm guessing it starts at 
providing a new method for the non-standard-class class, but I'm at a 
loss how to proceed any further.

thanks!
-Yves Vandriessche

From: Pascal Costanza
Subject: Re: change-class with non-standard-class metaclasses
Date: Sat, 08 Jul 2006 13:12:12 +0000
Message-ID: <4h9p9dF1q4gdcU1@individual.net>

Yves Vandriessche wrote:
> Say I want to convert a simple rectangle class to a different one, such 
> as the gdk:rectangle class to be used in a wrapper.
> 
> (change-class my-rectangle 'gdk:rectangle)
> 
> The problem here is that the gdk wrapper library specifies its own 
> meta-class for gdk:rectangle, instead of using standard-class.  This 
> means that the method selection for change-class fails.

That doesn't necessarily have to be the case. How is change-class 
specialized?

> How could I work around this problem?  I'm guessing it starts at 
> providing a new method for the non-standard-class class, but I'm at a 
> loss how to proceed any further.

I see the following possible workarounds:

- Use that other metaclass for your own rectangle class.
- Ask the provider to use standard-class.
- Use a wrapper object. Then you can replace the old instance with a new 
instance, instead of using change-class.


But I don't see yet why change-class would fail.

Pascal

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