This is a very interesting point and should be highlighted. You said implementation artifacts (especially in reference to reducing code duplication), and for clarity, I think you are referring to the definition of operators on data (class methods, friend methods, and so on). I agree with you that subclassing (for the purpose of reusing behavior), traits (for adding behavior), and the like can be confused with classification to such an extent that modern designs tend to depart from type systems and be used for mere code organization.