What would be the alternative? One program-wide generic object?

sub id { Scalar::Util::refaddr( shift) || 'the_one_generic_object' }
[download]

would do that. So would the standard id() function (ignoring possible "uninitialized" warnings) with an empty string instead of 'the_one_generic_object".

I wouldn't put it in terms of "right" and "wrong", but obviously I expect the behavior that has one generic object per class to be more useful. I'd have to build, or at least sketch, some example applications that involve subclassing to see which behavior wins out in practice. At this point it's just my intuition, but I'm not alone in that. In his perltooc, Tom Christansen discusses a similar concept for the standard hash-based type of class. The functional equivalent of the generic object is what he calls the eponymous hash. That implementation also provides one such hash per class.

Anno