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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Does object renaming allow the view to be a copy?
Date: Mon, 23 Jan 2017 14:40:08 -0600
Organization: JSA Research & Innovation
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Date: 2017-01-23T14:40:08-06:00
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"G.B." <bauhaus@notmyhomepage.invalid> wrote in message 
news:o61qau$ock$1@dont-email.me...
>A SO answer (41746244) has given rise to the question of whether
> or not a compiler implementer may make a renamed object a copy
> of the original. (Layman's assumptions from LRM 3.1(7), 8.5.1),

Logically, the item is not a copy. How the compiler implements that, 
however, is its business.

> So, is the following program, modifying compoments of and array,
> ever allowed to raise Renaming_Is_Copying?

Of course. The program has nothing to do with copying that I can see.

...
>         begin
>             if X'Address = Stuff (K)'Address then

The meaning of X'Address is implementation-defined (as someone said, 
consider what happens if X is allocated in a register). It's best if its use 
is limited to the sort of low-level purposes for which it was defined (that 
is, handling memory-mapped hardware). Note in particular 13.3(16): if the 
objects in question aren't "aliased", the result of 'Address may not be 
"useful".

If the objects are aliased, then you don't need to use 'Address to get the 
answer to your question:

             if X'Access = Stuff (K)'Access then

would answer your question (but you might need to declare an appropriate 
access type somewhere). Note that the compiler would strip off any funny 
business for this latter case.

IMHO, 'Address should only appear in a program that is interfacing to some 
memory-mapped entity; else use some form of 'Access (or 'Unchecked_Access).

                                     Randy.