...

int main() { boost::shared_ptr<Doc> lp_doc( new Doc );

std::copy(lp_doc->foo().begin(), lp_doc->foo().end(), std::ostream_iterator<double>(cout, " ") ); cout << endl; }

`std::vector& Doc::foo()' is protected

This is not a shared_ptr problem. The same thing would happen if you were using Doc *. You could fix it by using Doc const *, and in the shared_ptr case you can fix it by using boost::shared_ptr<Doc const>.

Or you could fix the problem by using different names for the const and non-const foo() functions. Your original design shows some confusion about C++ rules about access control. Making something protected does not affect whether it's considered when doing overload resolution, so it's impractical to have a pair of const/not-const functions overloaded the way you do.

Using protected did show that the non const member was taken - a "furtune" for me of testing the public interface. Only the derived classes should use protected ( I did hide that part from snippet). I hoped, that std::copy takes the const iterators, after looking into the headers - it takes generell iterators. Thanks Olaf