[Zope-dev] Re: Future of ZClasses

[Philipp von Weitershausen]

Lennart Regebro wrote:
> On 9/29/06, Dieter Maurer <dieter at handshake.de> wrote:
>> You want to stick this interface to individual objects,
>> while Lennart proposed to stick it to a type and use
>> some kind of inheritance to make it effective on all objects
>> instantiated from this type.
>>
>> For me, Lennart's approach seems to be far more economic, as
>> he does things on an abstract (the type) level rather than
>> always work on the concrete (the individual object) level.
> 
> In fact it is absolutely necessary, as you want to be able to change
> the behaviour of a whole type of content classes. If you create the
> content class "Events" and then suddenly want all events to have a
> iCal export support, you do not want to enable this per event, but for
> the type "event".

That doesn't make it necessary. Let's say all event objects are marked 
with IEvent. Now you want to add behaviour to events. You can do that by 
registering stuff for IEvent. All objects marked with IEvent will get 
the new behaviour.

Why would a type be needed?

> The type is thusly equivalent to portal types of CMF.

Types in Zope 3 are typically expressed by interfaces. I think all of 
your use cases can be covered with just interfaces. No need to invent 
yet another thing that you'll have to persist and create machinery for.