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Jim Fulton wrote:

> On Dec 17, 2007, at 10:07 AM, Janko Hauser wrote:
> ...
>> This baffles me somewhat. At the moment I see skins/layers as the  
>> only mechanism to let developers using an application to customize  
>> it, possibly more than once in the same instance. I find them not  
>> optimal, because they only allow customizing on the outer most  
>> level. But overrides is a failure as I understand it.
> 
> How are overrides a failure?

For one thing, they don't let you turn *off* a feature;  you have to
provide an alternative.  Reusing naively-constructed ZCML from another
package is hard enough that I've begun *copying* it into 'etc' and
modifying it, rather than trying to juggle '<include>' and
'<includeOverrides>'.  I would still like to see the '<include>'
machinery extended to support "masking" (e.g., via 'only' and 'exclude'
subdirectives).

> Skins, after all do nothing but override views.

Skins provide a mechanism for defining views against more specific
interfaces, which is not what ZCML overrides do at all:  they replace
existing registrations.

>> So what should be used or invented instead?
>
> I use overrides.
> 
>> As a usecase take a forum application which should be installed more  
>> than once in an instance but needs different layouts and also  
>> different subset of functionality.
> 
> 
> I don't have this use case. I wonder how many people do.

It was a common use case under CMF, and remains one in Plone.

> We tend to think up complex use cases and then make the zope framework  
> more complicated to deal with them.  Sometimes these are legitimate  
> use cases, but they are rarely common cases and their solutions should  
> generally not be inflicted on the masses.
> 
> WRT this use case, I strongly suspect it would be simpler and easier  
> to support defining multiple configurations in ZCML and a mechanism to  
> specify different configurations for different sites within an  
> instance.  In fact, I think Stephan Richter added this a while ago.

Agreed.  For instance, I'm finding the IRO-based lookup mechanism to be
overkill for lots of applications, which basically just need a flat
namespace registry (a la entry points in eggs).


Tres.
- --
===================================================================
Tres Seaver          +1 540-429-0999          [EMAIL PROTECTED]
Palladion Software   "Excellence by Design"    http://palladion.com
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