Martijn> Oren Tirosh wrote: Oren> I propose that any method or attribute may serve as a Oren> marker. This makes it possible to use an existing practice as a Oren> marker so protocols can be defined retroactively for an existing Oren> code base. It's also possible, of course, to add an attribute Oren> called 'has_property_such_and_such' to serve as an explicit Oren> marker. Martijn> This is an interesting idea. I'd say you could plug such a Martijn> thing into an interface system, by making Martijn> 'interface.isImplementedBy()' calling some hooks that may Martijn> dynamically claim an object implements an interface, based on Martijn> methods and attributes. In that case, a marker is really just an interface with a single element. -- Andrew Koenig, ark@research.att.com, http://www.research.att.com/info/ark