Hi, I am aware of the problem, but never saw any study of it. Anyway, in my experience, starting with virtual functions does help with it. Virtual interface in fact forces clear interface/implementation separation and makes 'what goes where' question more a technical problem then a philosophical one. So starting with problems like 'write two objects with same virtual interface and a main program that handles both in uniform way' does help to grip the OO concept. Once the student has some basic understanding of it, it is possible to move to nonvirtual interfaces. Martin
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