//  Should be equal
void interop ( const std::string &str, string_ref ref ) {
//  BOOST_CHECK ( str == ref );
    BOOST_CHECK ( str.size () == ref.size ());
    BOOST_CHECK ( std::equal ( str.begin (),  str.end (),  ref.begin ()));
    BOOST_CHECK ( std::equal ( str.rbegin (), str.rend (), ref.rbegin ()));
    }