Hi Dima, > At least I don't see any options for multiple implicit conversion here. It seems to be one and single. I see three implicit conversions. std::auto_ptr<const A>::auto_ptr(std::auto_ptr_ref<const A>) ... via the operator cast std::auto_ptr<const A>::auto_ptr(std::auto_ptr<const A>&) ... by template constructor std::auto_ptr<const A>::auto_ptr(std::auto_ptr<const A>&) ... by copy constructor The "perfect match" would be... std::auto_ptr<const A>::auto_ptr(std::auto_ptr<const A>) ... but that does not exist. > I don't see neither multiple paths to do the conversion,nor sequence of conversions that require more than one cast. See above. The real issue is that a std::auto_ptr<const B> is *NOT* a std::auto_ptr<const A>, since std::auto_ptr<const B> is *NOT* derived from std::auto_ptr<const A>. The former is not interchangeable with the latter. HTH, --Eljay
