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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Access to interface conversion problem
Date: Tue, 13 Mar 2007 12:06:07 -0400
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msimonides@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.

C++ has a more powerful form of multiple inheritance than Ada does.
If we didn't care about interfacing, we could implement Ada without
this somewhat-strange offsetting of the addresses.

> To me this looks like a compiler bug.

Could be.

- Bob