Difference between revisions of "Transient Attributes"
(→‎Validity Rule)
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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 is not a user defined expanded type.
  
 
== Rationale of validity rule ==
 
== Rationale of validity rule ==

Revision as of 14:46, 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 is not a user defined expanded type.

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.

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