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Newsgroups: comp.lang.ada
Date: Sun, 11 Mar 2018 07:31:31 -0700 (PDT)
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Subject: Re: Ada Alternatives to Unrestricted_Access
From: Jere <jhb.chat@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:50927
Date: 2018-03-11T07:31:31-07:00
List-Id: <comp.lang.ada>

On Sunday, March 11, 2018 at 5:57:47 AM UTC-4, Jeffrey R. Carter wrote:
> On 03/11/2018 01:38 AM, Jere wrote:
> > On Friday, March 9, 2018 at 11:46:03 AM UTC-5, Jeffrey R. Carter wrote:
> >>
> >> OK, that's what I missed. I guess you could unchecked convert from
> >> access-constant to access-all.
> >>
> > My only concern with this is does the Ada language allow it portably?  I
> > know it works in GNAT, but what I couldn't find is if the RM allowed
> > for a constant variable to have a different internal representation than
> > a non constant version of the variable.  If that were the case, then I
> > would be worried that doing an unchecked_conversion (or an
> > Address_To_Access_Conversion) could provide an erroneous result.
>
>    <SNIPPED>
> 
> Why do you need this function?
> 
It's iterator related.  In order to iterate through a container in all
contexts, the Default_Iterator function needs a parameter of mode "in".
In order to leverage the anti tamper functionality, the iterator needs
a non constant access to the container to be supplied when building
the iterator inside the Default_Iterator function (so it can modify
the tamper state of the container).  The GNAT body for the Vectors 
package has an example (I think it is a-convec.adb, just search for
"function iterate" and look for the one that returns an iterator).