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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Assignment access type with discriminants
Date: Thu, 23 Mar 2023 12:51:03 +0100
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On 2023-03-22 15:10, G.B. wrote:

> Some experiments point at the general access type.
> 
>     type Foo_Ptr is access Foo; -- sans `all`
>     X : Foo;
>     P : Foo_Ptr := new Foo;
>     type Foo1 is new Foo_Ptr (K => F1);
> begin
>     X := (F2, 1.0);   -- OK
>     P.all := (F1, 3); -- _no_ Error!
>     Foo1 (P).all := (F1, 3);
> end Test;

You get no error because you do not change the discriminant. Change your 
code to:

     P.all := (F2, 1.0); -- Error!

> (Doesn't rejection for general access types seem reasonable
> if assignment would otherwise require adjusting the storage
> layout of a variable, including all access paths to components?
> Just guessing.)

I guess that an implementation must allocate memory for any value unless 
you constraint the discriminants in a subtype. But I am not a language 
lawyer to judge.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de