One of the fundamental principles of OO is go for interface inheritance(design) as opposed to class inheritance(implementation). Better way to enable code reuse is through association. That is why languages like Java do not allow multiple class inheritance, but allow you to inherit from multiple interfaces. You are doing it the wrong way!
Very right. It is about how you think in terms of OO. If you feel the problem space cannot be modeled easily, just don't go for OO. That said, many problem spaces are amenable to OO thinking. But some are not (especially the ones that deal with serial hardware interfaces), just go for procedural thinking in these cases.
The problem is you really want to inherit the implementations as well -- otherwise every one of the classes that use the Isin interface must implement its storage and accessors as well.
You can just do both, though. Use interfaces for polymorphism, to define the interactions between your objects -- and then, if you want, use inheritance as one possible strategy for code reuse.
