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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Subject: Re: freeing general access types
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Date: Mon, 23 Dec 2002 23:35:37 GMT
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tmoran@acm.org writes:

> If P is a general access type, is there any way to know whether it's
> pointing to allocated storage, and should have Ada.Unchecked_Deallocation
> applied to avoid a memory leak, or it's pointing at a declared
> object, which should not be deallocated?

No, other than whatever logic is in your program to keep track.

Note that you also need to make sure you are deallocating from the right
pool.  If you have a value of a general access type, you do not
generally know that it was allocated from the pool of that type.
You must convert it to the right type before deallocating.

I have written pool types where you can tell at run time which pool (if
any) a given pointer is pointing into.  But the more common thing is to
encapsulate allocation and deallocation in a small place where you can
understand (at compile time) what's going on.

Many access types are not used for allocation/deallocation at all.
They are used only for 'Access and/or conversion from other types.
It's a good idea to write:

    for Acc_Type'Storage_Size use 0;

for such types; then you will usually get a warning if you try to do a
"new".  And a run-time error.

- Bob