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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
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Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: Wed, 6 Jul 2005 17:51:40 -0500
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Date: 2005-07-06T17:51:40-05:00
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"Pascal Obry" <pascal@obry.net> wrote in message
news:uk6k42wvf.fsf@obry.net...
>
> Martin Dowie <martin.dowie@btopenworld.com> writes:
>
> > I doubt if that Ada.Containers would be used in systems that have safety
> > concerns.
>
> I think Dmitriy has a good point. For the first time in Ada we have the
> possibility to create easily a dangling pointer using Cursor. This was not
> possible before except by using Unchecked_Deallocation.

I think the problem is an early implementation of the Containers library.

Perhaps I need to write a paper: "Matt Heaney's Container implementation
considered harmful." :-)

I strongly believe that the Containers implementations provided by default
with compilers should do some minimal checking for dangling cursors (that
is, err somewhat on the side of safety). Not necessarily going all the way
to perfect checking, but at least detect the obvious cases of dangling
cursors like the one given previously. OTOH, there will be cases where
implementations like Matt's are necessary -- but I'd prefer to call them
"Unchecked_Containers" and use them only when performance is critical.

                                     Randy.