On Behalf Of Ovanes Markarian On behalf of; Igor R [boost.lists@gmail.com] ---------------------------------------------------------------------------- ------------------- Thank you for your answers, But it may be boost::variant is not what I need, but perhaps a different facility implementing visitor pattern. My restriction is that f takes a ABC const-ref as an input. Can I construct the variant from the const ABC& abc Maybe like variant<D1, D2, ... Dn> v(abc); without deep copying. The Di objects are big. Then I would apply the visitation. Maybe storing variant<D1*, D2*, Dn*>... So f would look like void f( const ABC& abc ) { const VariantTypeDefProvidedByLib v(&abc); v.apply_visitor( YourVisitor ); } If this works, what is its cost relative to having been able to simply implement virtual functions in ABC? Again, thanks for the answers, Regards,