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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
References: <oghf54-6ho.ln1@hal.boavista.snafu.de> <45853BDC.5000902@obry.net>
 <sa43b7dx4eb.fsf@margay.local> <4586FAC4.2000003@snafu.de>
Subject: Re: How to get around "access type must not be outside generic unit"
Date: Mon, 18 Dec 2006 14:57:15 -0600
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Date: 2006-12-18T14:57:15-06:00
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"Michael Erdmann" <michael.erdmann@snafu.de> wrote in message
news:4586FAC4.2000003@snafu.de...
> Brian May wrote:
...
> > I would have thought since Install was defined within the generic
> > unit, Install'Access would be OK.
> >
> > Or does Install'Access imply a temporary local variable?
> >
> > Put another way, how can you create a dangling pointer with
> > Install'Access but not Install_Access?
>
> This is exactly what came into my mind when i was looking
> at the offending code.

Jean-Pierre explains it well. If you instantiate the generic inside a
procedure, the access value could last longer than the procedure it points
at. That's a no-no. Since generic bodies use "assume-the-worst" legality
rules, it is illegal because it *might* happen.

It should be noted that this rule dates back to Ada 95 (although it was
poorly described in Ada 95). AI95-229 explains the issues, find it on
www.ada-auth.org.

               Randy.