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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Language lawyer question: Equality on 'Access attributes
Date: Sat, 10 Jan 2004 12:56:44 +0100
Organization: At home
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Robert A Duff wrote:

> Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> writes:
> 
>> What is the "expected type" in the case of X'Access = Y'Access? There
>> is no one! So I think that GNAT formally does not contradict the
>> standard.
> 
> The expected type is the type of the formal parameter of "=".
> There is only one such "=" of interest, and its formal parameter
> has type Ptr1.

Just summarizing...

Your point is that the compiler should consider all visible types and all
visible "=" to crunch X'Access = Y'Access. Then X'Access = Y'Access is
illegal if there is no visible named access types. Then provided:

type A is tagged null record;
type A_Ptr is access all A;
function "=" (Left : A_Ptr; Right : access A) return Boolean;
X : aliased A;
Y : aliased A;

X'Access = Y'Access -- is ambiguous

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de