Optional makes an object with destination address for column value with name columnName # If column value is NULL, then ScanNamed will write a nil into destination Warning: value must double-pointed data destination.

OptionalWithDefault makes an object with destination address for column value with name columnName If scanned YDB value is NULL - default type value will be applied to value destination Warning: value must single-pointed data destination.

Required makes an object with destination address for column value with name columnName Warning: value must single-pointed data destination.