Thanks, that makes sense. IIRC, I read about this either in Bertrand Meyer's book Object-oriented Software Contruction, or in the Eiffel language's docs, some y

Thanks, that makes sense. IIRC, I read about this either in Bertrand Meyer's book Object-oriented Software Contruction, or in the Eiffel language's docs, some years back, though I may not have known about it as an application of the Liskov substitution principle at the time, or even later, although I did read about the Liskov principle later :) And I may not have grokked the Liskov principle when I read it, either, but thanks to your reply, I now have a glimmering of what it means, and will look it up again :)