Function interp_set_old_class 

fn interp_set_old_class(
    _args: &[RValue],
    _named: &[(String, RValue)],
    _context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Set old-style S3 class for S4 compatibility.

@param Classes character vector of class names @return invisible NULL @namespace methods