The diamond example "TA extends Student, Teacher" seems worse than OO or direct composition. It's either a compiler error or share everything that overlaps. I

The diamond example "TA extends Student, Teacher" seems worse than OO or direct composition. It's either a compiler error or share everything that overlaps. I would have made the sharing explicit during composition--a Teacher or Student is given the Person instance when constructed, so sharing or not sharing is decided at composition time. To enforce consistency use helper/static methods.