That's not general [implementation] inheritance, it's just delegation. The problematic, non-compositional feature of implementation inheritance is something known as open recursion, viz. the fact that every call to an overridden method like .move(...) - importantly, even a call that's merely a private implementation detail of some code in the base class - goes through an implied dispatch step that introduces a dependency on the actual derived class instance that the base-class method is being called on. This creates the well-known "fragile base class" problem since method calls to these possibly-overridden methods are relying on fragile, unstated invariants that might be broken in the derived classes, or altered in future versions of the base class.