>>>>> "Y" == Yukihiro Matsumoto <matz / zetabits.com> writes: Y> class B<Array; end Y> a = A[1] + B[2] Y> What do you expect? A? B? Array? Array and with class B < A end B[1] + B[1] # B B[1] + A[1] # A B[1] + [1] # Array A[1] + A[1] # A A[1] + [1] # Array Guy Decoux