From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,ed6a891101ff4e06
X-Google-Attributes: gid103376,public
From: Niklas Holsti <nholsti@icon.fi>
Subject: Re: Freeing Pointers to classwide types
Date: 1998/10/11
Message-ID: <362081E9.5CF38122@icon.fi>#1/1
X-Deja-AN: 399897881
Content-Transfer-Encoding: 7bit
References: <1ftmFTC69GA.191@samson.airnet.net>
 <m3r9wjvt6c.fsf@mheaney.ni.net> <361E65A8.36082B5D@icon.fi>
 <m3r9whuzak.fsf@mheaney.ni.net>
Content-Type: text/plain; charset=us-ascii
Organization: Space Systems Finland Ltd
Mime-Version: 1.0
Newsgroups: comp.lang.ada
Date: 1998-10-11T00:00:00+00:00
List-Id: <comp.lang.ada>

Matthew Heaney wrote:
> 
> Niklas Holsti <nholsti@icon.fi> writes:
> 
> > Matthew Heaney wrote:
> >   [snip]
> > >
> > >    type T_Access is access all T'Class;
> > >    for T_Access'Storage_Size use 0;
      [snip]
> > In fact, the above code elicits the following message from GNAT:
> > "Warning: implicit call of Initialize will raise Storage_Error."

First, let me correct myself: GNAT actually warns that the implicit
Initialize call will raise Program_Error, not Storage_Error.
Moreover, this occurs with a rather old GNAT version (3.05); the
version in WebAda does not emit this warning, so it was probably a
fault in the old GNAT. Sorry for this confusion.

> If you call new for an access type whose storage size is 0, then you'll
> get Storage_Error.

I don't think the LRM says precisely that. Storage_Error is raised
if there is not enough storage, but defining Storage_Size
as zero does not mean that the available storage is zero, since the
compiler can make the storage pool larger than requested. Of course
this may be an insignificant quibble, if all compilers actually
provide exactly the requested size.

On the other hand, it seems that GNAT (in WebAda) lets one specify
a positive Storage_Size for an access type to a descendant of the
type T, so it would seem possible for clients to use "new" for
descendant types. Doesn't this break your approach?

- Niklas