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From: Niklas Holsti <nholsti@icon.fi>
Subject: Re: Freeing Pointers to classwide types
Date: 1998/10/09
Message-ID: <361E65A8.36082B5D@icon.fi>#1/1
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Date: 1998-10-09T00:00:00+00:00
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Matthew Heaney wrote:
  [snip]
> I like each specific type in the hierarchy to maintain its own free list
> of already-allocated objects.  Provide a class-wide operation that
> dynamically dispatches a private Do_Free op.  Something like:
> 
> package P is
> 
>    type T is abstract null record;
                      (* need "tagged" here)
> 
>    type T_Access is access all T'Class;
>    for T_Access'Storage_Size use 0;
>    --
>    -- By making this have a storage size of zero, you force
>    -- clients to call a constructor (allocator) for the specific
>    -- type.

I don't see how the commented statement follows from the LRM text on
the Storage_Size attribute. I'm looking mainly at LRM 3.11(18), which
says that the actual size with be _at least_ the one specified, so
even though you specify zero, the size could be a million units.
In fact, the above code elicits the following message from GNAT:
"Warning: implicit call of Initialize will raise Storage_Error."

Could you explain how your suggestion works?

Niklas Holsti