Difference between revisions of "Transient Attributes"
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== Validity Rule == | == Validity Rule == | ||
| − | An attribute can be marked `volatile' if and only if its type has a default value | + | An attribute can be marked `volatile' if and only if: |
| + | # its type has a default value | ||
| + | # it is not a user defined expanded type | ||
| + | # the enclosing class is not expanded | ||
== Rationale of validity rule == | == Rationale of validity rule == | ||
If the type did not have a default value (which is the case for attached types), then upon retrieval the volatile attribute would be Void which is against void-safety. | If the type did not have a default value (which is the case for attached types), then upon retrieval the volatile attribute would be Void which is against void-safety. | ||
| − | For simplicity and backward compatibility of `basic_store' which does a memory copy of the object to disk, it would be quite complicated to implement when | + | For simplicity and backward compatibility of `basic_store' which does a memory copy of the object to disk, it would be quite complicated to implement when expanded are involved. We prefer our users to use SED once it supports expanded. |
Revision as of 15:16, 23 June 2009
For storable purposes, it makes sense that some attributes of objects are not stored to disk. We call them volatile attribute and currently are specified using a note clause:
field: detachable X note option: volatile attribute end
Validity Rule
An attribute can be marked `volatile' if and only if:
- its type has a default value
- it is not a user defined expanded type
- the enclosing class is not expanded
Rationale of validity rule
If the type did not have a default value (which is the case for attached types), then upon retrieval the volatile attribute would be Void which is against void-safety.
For simplicity and backward compatibility of `basic_store' which does a memory copy of the object to disk, it would be quite complicated to implement when expanded are involved. We prefer our users to use SED once it supports expanded.
