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From: dewarr@my-dejanews.com
Subject: Re: Freeing Pointers to classwide types
Date: 1998/09/28
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In article <360f143c.39974468@SantaClara01.news.InterNex.Net>,
  tmoran@bix.com (Tom Moran) wrote:
> > it is actually quite easy
> >in Ada 95 to do exactly what you want. You probably aren't familiar with
> >the Storage_Pool facility -- many Ada programmers don't know this very
> >powerful feature in the language well enough, but read up on it, you will
> >find it allows you to do exactly what you want in a completely portable
> >manner.
> Deciding to use Storage Pools does not fall within my definition of
> modest changes to a program.
>   In any case, is it required that a compiler that does not free
> memory when an access type goes out of scope, must free the memory if
> the access type is to a user controlled storage pool?  That's not
> obvious to me from reading the RM.  Or would the procedure declaring
> the access type also have to declare an instance of the user defined
> storage pool?  And if the reason not to use a compiler that frees the
> storage is that it's expensive, is the user defined storage pool
> technique cheap?


You really should look at the Storage_Pools facility. You seem to be declaring
that you are sure it is not a modest change, but then ask questions that
suggest you are not quite sure what such a change would involve. In the case
of GNAT, it is just a matter of adding a single representation clause for the
type, not a big burden.

The point about using Storage_Pool's is not that it eliminates the overhead,
of course it does not, since there is no magic way of doing this, but that
you only pay this overhead if you want.

I find nothing in what you are saying that would seem to justify adding this
additional overhead unconditionally. Indeed, the less magic going on the
better as far as I am concerned.

Once again, the expectation here that a compiler will free all storage
associated with local allocators on scope exit is not justified. It is
no more or less justified than expecting that you will find a complete
garbage collector (after all this is just a special case of automatic
garbage collection, why single it out?)


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