in reply to inheritance turns back and bites

  1. The $answer object is using its own method instead of SomeData's method
  2. Use Class::MultiMethods, or less elegantly 
    sub add {
  @_ > 2 && return $_[0]->SUPER::add(@_[1 .. $#_]);
  ...
}

    [download]
  3. Don't use parameter based dispatch in perl ;)
HTH

_________
broquaint

In Section Seekers of Perl Wisdom