field_cmp
cmp = field_cmp(get_field(a), get_field(b));
ret = field_cmp(fields_a[idx], fields_b[idx]);
ret = field_cmp(fields_a[i], fields_b[i]);
ret = field_cmp(get_field(a), get_field(b));
ret = field_cmp(fields_a[i], fields_b[i]);
ret = field_cmp(get_field(a), get_field(b));