( $type, $value ) = $object->invoke_t($operation, .. args .. )>
Invokes the named class operation on the object in the same way as invoke(), but invoke_t() also returns the type of data returned by the call.
The data types are encoded as integer numbers. If the return is an array, then the $value will receive a reference to the array. If the return is a scalar, then $value will hold it.