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

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