[ZODB-Dev] Implementing Storage Decorators

[Tino Wildenhain]

Dieter Maurer schrieb:
> Jim Fulton wrote at 2007-5-4 14:40 -0400:
>> On May 4, 2007, at 2:33 PM, Dieter Maurer wrote:
>>
>>> Jim Fulton wrote at 2007-5-2 11:52 -0400:
>>>> ...
>>>> I think I still rather like explicit, but I'm on the fence about
>>>> which approach is best.  What do other people think?
>>>> From your description, I would use a subclassing (and forget about
>>> proxy and copying).
>> That would be a nightmare, on multiple levels:
>>
>> - All of the separate implementations would become tightly coupled,  
>> which is what happens with inheritance.
>>
>> - Either someone would have to create classes for the various  
>> permutations of features, or consumers would have to mix and match  
>> multiple classes to get what they want and sort out the variate  
>> internal implementation incompatibilities.
> 
> Your decorators would become mixin classes
> and the final classes would list the features they like -- simpler
> than ZCML binding together...
> 
> Of course, some features may not play well with one another.
> But, that will make problems also with proxies or copying...

Even this could be sorted out with special cleanup or
secure mixins which can do dirty tricks like accessing
self.__class__.__bases__ to fixup ;) (Much like combining
the copy with the subclass approach)

I'm for mixin with strong guidelines on implementation
(e.g. how to call private attributes to not pollute the
  namespace)

Regards
Tino