Difference between revisions of "Transient Attributes"
(New page: 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: deta...) |
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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: | 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: | ||
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field: detachable X | field: detachable X | ||
note | note | ||
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attribute | attribute | ||
end | end | ||
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== Validity Rule == | == Validity Rule == | ||
An attribute can be marked `volatile' if and only if its type has a default value and if the enclosing class is not expanded. | An attribute can be marked `volatile' if and only if its type has a default value and if the enclosing class is not expanded. | ||
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| + | == 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. | ||
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| + | 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 14:37, 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 and if 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.
