Re: Access to interface conversion problem

["Adam Beneschan" <adam@irvine.com>]

On Mar 13, 9:06 am, Robert A Duff <bobd...@shell01.TheWorld.com>
wrote:
> msimoni...@power.com.pl writes:
> > The output of this program is two addresses, the first one 4 less than
> > the second one (in my original program the difference is 12).
> > Removing the Root_Implementation_Type tagged type from inheritance
> > hierarchy results in identical addresses.
>
> > The question is:
> > Am I doing something wrong with the conversion?
>
> I don't know (I didn't read your code carefully), but it is normal for
> access values pointing at the same object to be represented by different
> addresses, depending on which interface you are viewing the object as.
> This is because C++ works that way, and GNAT mimics the C++ conventions
> in order to make interfacing Ada with C++ easier.

I still think 'Address should be the same, though.  The definition of
X'Address for an object X is that it is "the address of the first of
the storage elements allocated to X"; and here, after IFace_Ptr has
been converted from Object_Ptr by a legal type conversion,
IFace_Ptr.all and Object_Ptr.all are the same object, so their
'Address should be the same.  It may be the case that IFace_Ptr and
Object_Ptr are represented as different addresses in memory, and that
if you used an Unchecked_Conversion on the access objects themselves,
you might see different values.  But Marcin's code didn't use
Unchecked_Conversion; the 'Addresses should be the same, and if the
addresses stored in memory are different, the compiler needs to adjust
for this when computing 'Address.

This definitely seems like a compiler bug.

                                  -- Adam