[elephant-ticket] #47: Handle derived index errors caused by missing slots in a redefined class

[elephant]

#47: Handle derived index errors caused by missing slots in a redefined class
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 Reporter:  ieslick       |       Owner:  ieslick      
     Type:  defect        |      Status:  new          
 Priority:  major         |   Milestone:  Release 0.9.1
Component:  metaprotocol  |     Version:               
 Keywords:                |  
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 Derived indices depend on a class instance for their value.  This usually
 means they perform some computation over slot values.  What happens when a
 slot is removed, but the index is not?  Today it will provide a
 nonsensical error message about a non-applicable generic function.

 - We can ensure that the dependencies of a derived index are maintained
 explicitly so the deletion happens automatically (see
 - We can provide a sensible error message with restart options that
 removes the failing derived index

 This should be tied up in a ticket to only update derived indexes when
 slots they depend on are updated.

 My plan is: support hints, do auto updates when hints indicate a lost
 dependency, otherwise provide an interactive, restartable error to remove
 the derived index.

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Ticket URL: <http://trac.common-lisp.net/elephant/ticket/47>
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