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From: Jacob Sparre Andersen <jacob@jacob-sparre.dk>
Newsgroups: comp.lang.ada
Subject: Re: Generic private type declaration
Date: Sat, 26 Nov 2016 09:45:32 +0100
Organization: JSA Research & Innovation
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Date: 2016-11-26T09:45:32+01:00
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Alejandro R. Mosteo wrote:

> I need some eyes on this error because I'm missing something
> basic. When compiling this code:
>
> procedure B001_Tagged is
>
>    generic
>       type X is private;
>    package Untagged is
>
>       type Y is new X;
>
>    end Untagged;
>
>    package Ok is new Untagged (Integer);
>
>    type Void is tagged null record;
>
>    package Err is new Untagged (Void); --  Error here
>
> begin
>    null;
> end B001_Tagged;
>
> I get in both gnat 4.9.3 and gpl2016 the following error:
>
> b001_tagged.adb:15:04: instantiation error at line 7
> b001_tagged.adb:15:04: type derived from tagged type must have extension
> gnatmake: "b001_tagged.adb" compilation error
>
> I would expect that the view inside the generic package is untagged
> and so the type renaming in line 7 should be correct?

I agree with your expectation.

I suspect that this is an error due to how GNAT expands generics.  It
might be useful to try to see how Janus/Ada and ICC/Ada treats it.  If I
remember correctly, Janus/Ada implements generics differently from GNAT.

Greetings,

Jacob
-- 
"... but I don't think even Tucker can do scheduling with no cost."
                                                  -- Randy Brukardt