mpty base classes can be
    allocated at the same offset, provided that none of them have a common
    ancestor (see section 10.5 [class.derived] paragraph 5 of the standard).
    But the language definition also doesn't <em>require</em> implementations
    to do the optimization, and few if any of today's compilers implement it
    when multiple inheritance is involved. What's worse, it is very unlikely
    that implementors will adopt it as a future enhancement to existing
    compilers, because it would