Re: Ada 0Y plans for garbage collection?

["Robert I. Eachus" <rieachus@attbi.com>]

Martin Krischik wrote:

>>I still think the way it was done in Modula-3 gives you the best of
>>both worlds. If you want garbage collection, you allocate from a
>>different pool. If you don't want it you don't use it, and there is no
>>overhead.
> 
> Well, you can have this allready at least with GNAT. See
> http://www.ada.krischik.com for details.

Exactly.  And if you read the documentation there, you eventually 
conclude that a garbage collected pool for Ada implementations may seem 
like a good thing, but it creates more issues than it solves.  It can be 
done, and it has been done.  But in practice building reference counts 
into types which need garbage collection gives you much better control 
over finalization.

And yes, I know that there are general graph structures where reference 
counts don't work.  I also know that in practice most such general 
graphs can be constructed with structural pointers and general pointers 
so that the structural pointers define a tree and nodes not in the tree 
should be reclaimed. You could say that doing that is a lot of extra work.

It is a lot of work.  But in the cases where I have run into this issue, 
the graph partitioning was part of a proof of correctness that I really 
needed to be able to do anyway.  (Note that this is a proof of 
correctness of the algorithm to be implemented, before I ever got to 
writing code.)

-- 
                                              Robert I. Eachus

"As far as I'm concerned, war always means failure." -- Jacques Chirac, 
President of France
"As far as France is concerned, you're right." -- Rush Limbaugh