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=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!nntp-feed.chiark.greenend.org.uk!ewrotcd!newsfeed.xs3.de!io.xs3.de!news.jacob-sparre.dk!franka.jacob-sparre.dk!pnx.dk!.POSTED.rrsoftware.com!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Convert an access to constant to access to variable
Date: Fri, 4 Aug 2017 19:26:27 -0500
Organization: JSA Research & Innovation
Message-ID: <om33bk$f3c$1@franka.jacob-sparre.dk>
References: <om2rph$18jt$1@gioia.aioe.org>
Injection-Date: Sat, 5 Aug 2017 00:26:28 -0000 (UTC)
Injection-Info: franka.jacob-sparre.dk;
 posting-host="rrsoftware.com:24.196.82.226";
	logging-data="15468"; mail-complaints-to="news@jacob-sparre.dk"
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.7246
Xref: news.eternal-september.org comp.lang.ada:47598
Date: 2017-08-04T19:26:27-05:00
List-Id: <comp.lang.ada>

"Victor Porton" <porton@narod.ru> wrote in message 
news:om2rph$18jt$1@gioia.aioe.org...
> What is the proper way to convert an access to constant to access to
> variable? (Yes, I know that then I need to be careful not to modify this
> "variable".)

Well, it's not a proper conversion, so there isn't going to be a "proper" 
way.

> Maybe Unchecked_Conversion?

That's one possibility.

> But:
>
> 1. Is Unchecked_Conversion guaranteed by the standard to work well in this
> case?

I think so. The rules for what must work are found in 13.9(5-10). I suppose 
a compiler could represent access-to-constant and access-to-variable 
differently.

In any case, your program is erroneous if it tries to write a constant. (But 
you knew that.)

> 2. Is there a simpler way than Unchecked_Conversion?

The alternative (assuming the access-to-variable is a general access type) 
is to use 'Access to convert:

     Ptr.all'Access

Nope, that won't work, because Ptr.all is a constant, and the result here 
has to be a variable in order to assign it into an access-to-variable.

You could certainly use Address_to_Access_Conversions, but whether that's 
"simpler" is in the eye of the beholder. (It also requires an instantiation, 
and usually an extra type conversion.)

                             Randy.