template <typename T>
class implicit_veneer
  : public S
  , is_veneer<S, implicit_veneer<S> >
{
public:
  typedef S                       parent_class_type;
  typedef typename S::value_type  value_type;

  // Other methods, including constructors
  ...

  operator value_type const *() const
  {
    return parent_class_type::c_str();
  }
};