Re: GCC 4.0 Ada.Containers Cursor danger.

["Randy Brukardt" <randy@rrsoftware.com>]

"Matthew Heaney" <matthewjheaney@earthlink.net> wrote in message
news:uslyrv50w.fsf@earthlink.net...
> To make things absolutely bullet-proof, I think you'd need at least a
> per-element reference count.  (That, or have the container maintain a
> list of extant cursors, which you would then have to search.)  If you
> attempt to delete a node for which the ref count is greater than 0, then
> you could raise an exception.  (This might actually produce a false
> positive, since the real error is attempting to dereference the cursor,
> not merely delete the node to which it is bound.  But to solve that,
> you'd have to move the node onto a free list, and during the dereference
> check to see whether the node is on the free list or not.)

It just struck me that this implementation would be wrong. The execution
doesn't become erroneous until the programmer uses the dangling cursor.
Raising some exception before the execution becomes erroneous wouldn't be
right.

I think that a scheme where the cursors were all linked to the container (or
element) would be needed to be completely bullet-proof (and correct). Then
the cursors could be marked as deleted when the element deleted or the
container is finalized. But that could have a lot of overhead.

                       Randy.