Re: Ada and string literals

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Adam Beneschan <adam@irvine.com> writes:

> On Wednesday, January 30, 2013 6:23:08 PM UTC-8, Robert A Duff wrote:
>
>> '[Unchecked_]Access is about object identity.
>> On the other hand 'Address is not -- two objects can have
>> the same address without being the same object.
>
> However, if two objects have the same 'Address, it's hard to imagine
> them not having the same 'Access as well, in practice.

It's easy to imagine that 'Access is illegal.  ;-)  That was part of my
point: a compiler can place two objects at the same address if
they are not aliased.  For example, if one of them has zero size.
And I wasn't thinking about the case where the user FORCES the
same address as in your example below.

>...  There aren't many cases where this is an issue, but:
>
>    procedure P (Addr : in System.Address) is
>
>       X : aliased T;
>       for X'Address use Addr;
>       pragma Import (Ada, X);
...
> Assuming T is a simple record type, for instance, I can't imagine
> XA=YA being false in any implementation, even though I believe X and Y
> are distinct objects by the RM's definitions.

For sure.  Are X and Y distinct objects?  I'd say the correct
answer is "Who cares?"  ;-)  Maybe this is a bug in the RM,
but I hope nobody pesters the ARG about it.  IMHO, bugs in the
RM should be reported to ARG only if fixing them would change some
compiler writer's behavior, or change some programmer's behavior.

- Bob