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From: Richard D Riehle <laoxhai@ix.netcom.com>
Subject: Re: Freeing Pointers to classwide types
Date: 1998/09/28
Message-ID: <6uojcq$bp2@sjx-ixn3.ix.netcom.com>#1/1
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Organization: ICGNetcom
X-NETCOM-Date: Mon Sep 28 11:09:30 AM PDT 1998
Newsgroups: comp.lang.ada
Date: 1998-09-28T11:09:30-07:00
List-Id: <comp.lang.ada>

In article <6uo83j$dv2$1@nnrp1.dejanews.com>,
	dewarr@my-dejanews.com wrote:

In reply to a question from Tom Moran about System.Storage_Pools (ALRM
13.11),

>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.

I checked the GNAT documentation. Am I missing something, I wonder?  Does
GNAT already include an overloading of the subprograms in
System.Storage_Pool.  If so, Robert's assertion that "it is just a matter of
adding a single representation clause" might be sufficient.  Otherwise, it
is a bit misleading in its suggestion of simplicity.

The representation clause is only a small part of the requirement for
using the abstract class package System.Storage_Pools.  One must also
overload the Allocate and Deallocate procedures.  In fact, to make this
package really useful, one must also overload the initialize and finalize
procedures from Ada.Finalization.  

There are very few examples in the literature for using 
System.Storage_Pools.  At several Ada conferences I asked prominent
technical experts if they could point me to some references where someone
had actually implemented an overloading  of System.Storage_Pools.  None of
those I asked were forthcoming.  The example in the Rationale falls into the
category of "seduced and abandoned."

More recently, John Barnes, dependable Ada stalwart, included an excellent
example in the Second Edition of his book, Programming in Ada 95.  It is
fully coded, readable, and enlightening.  However, it is clear from studying
the Barnes example that System.Storage_Pools is, in practice, a non-trivial
issue.   

Richard Riehle
richard@adaworks.com
http://www.adaworks.com