[Zope3-dev] Re: adaptation based on class rather than interface

[Martin Aspeli]

Jean-Marc Orliaguet wrote:

> And there is nothing wrong with using inheritance when there is a '__IS 
> A __' type of relation (e.g. an ordered folder IS A folder IS AN item, 
> ...), or if there is a HAS_A type of relation (a folder has items, a 
> chair has four legs...). It seems that Zope3 has banned all form of 
> class inheritance, even those that made sense, and that would have 
> simplified the implementation.

That is totally, utterly, patently rubbish. Devise some regular 
expression and grep the zope 3 source code for inheritance.

> "marker interfaces" have empty specifications, that's the problem: they 
> can't grow into "real" interfaces that have a specification. If you add 
> methods to the marker interface you will have to track down all classes 
> that implement the interface (unless you don't really care whether 
> classes do implement their interface).

Marker interfaces by design serve a different purpose than other 
interfaces. They are the equivalent of an on/off switch about object 
behaviour or purpose that is externalised from that object (i.e. they 
are not just booleans in a schema, they are potentially managed outside 
that class).

Martin