[EMAIL PROTECTED] writes: > I've recently been discussing the guideline recently added to the exceptions > policy page with Dave Abrahams and he has asked me to post my views here. > > There is a seductive form of arguement that I've seen repeatedly lead > projects into trouble which has made me very suspicious of the form: > "provide X because someone might want to do Y". One common example is > "provide public access to member data because someone might need to do > something with the members that isn't supported directly". (I hope that > this is a forum that would reject this argument.) Another arguement I've > encountered recently is that "all classes should have a virtual destructor > because someone may want to specialise them". > > The arguement is especially seductive when the cost of "providing X" is > either small or hidden. But many a project has failed through creeping > featuritis driven by such concerns. The cost of virtual inheritance from > std::exception may well appear small - indeed, most of it is the > intellectual cost of understanding the intent. > > Arguments of this form need to be challenged on the basis of whether "to do > Y" is a reasonable expectation. If not, then the solution isn't "provide X" > it is "discourage Y". > > Now, unlike the examples cited above, I've *never* encountered anyone > arguing that exception hierarchies should be designed to support MI in a > real design scenario. Nor, when challenged on this point, has Dave. The > hypothetial example cited seems very implausible: when developing a > subsystem to meet two interfaces I invariably develop a pair of adaption > wrappers over the core functionality. (And, in general, repackaging of > exceptions is a very small part of that wrapper.)
Alan, did you read http://aspn.activestate.com/ASPN/Mail/Message/boost/1781628 ?? FWIW, the rest of the thread is http://aspn.activestate.com/ASPN/Mail/Message/boost/1777712 > The obvious conclusion from the example cited is "don't multiply > inherit from classes that are not designed to support it". > > I'm always willing to learn, but in the absence of a compelling > example that MI is useful in exception heirarchies, I am unwilling > to support the new guideline. I'm feeling ambivalent about it now, but I do think Bjarne's example is a pretty good one, and I wouldn't guess he'd claim it happens "often" without some evidence. -- Dave Abrahams Boost Consulting www.boost-consulting.com _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
