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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada Successor Language
Date: Fri, 29 Jun 2018 15:47:29 -0500
Organization: JSA Research & Innovation
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Xref: reader02.eternal-september.org comp.lang.ada:53448
Date: 2018-06-29T15:47:29-05:00
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"Alejandro R. Mosteo" <alejandro@mosteo.com> wrote in message 
news:pgqtk8$avk$1@dont-email.me...
> On 25/06/2018 14:41, J-P. Rosen wrote:
...
>> The same derivation would not compile in the body of the generic, where
>> the worst is assumed
> GNAT 7.3/2018 does compile it if I move it to the private part or body, 
> which thus must be a bug, as hinted by that it allows taking the type's 
> 'Class...
>
> procedure Blah is
>
> generic
> type Something is private;
> package Duh is private type Meh is new Something;

-- This is legal, as I noted earlier. This is legal because there is no 
place where the type is both known to be tagged and known to be untagged. 
Inside this generic, the type is untagged.

> function Yes (M : Meh) return Boolean is (True);
> function Yes_Class (M : Meh'Class) return Boolean is (True);

-- This is *illegal*, Meh is not a tagged type. If GNAT is allowing this, it 
is a compiler bug.

> end Duh;
>
> type Oh is tagged null record;
>
> package Ouch is new Duh (Oh); -- This fails with non-tagged formal

This should work, assuming that the (illegal) 'Class is not included.

> begin
>    null;
> end Blah;

I suggest a GNAT bug report.

                            Randy.