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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: GCC 11 bug? lawyer needed
Date: Thu, 06 May 2021 21:02:54 +0100
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"Randy Brukardt" <randy@rrsoftware.com> writes:

> I agree that the original author of that program should not have used 
> "aliased" in the way that they did (they don't need the special semantics), 
> but we realize that some people would prefer to *explicitly* mark things as 
> aliased when they are going to take 'Access (and not worry about the type of 
> the parameter -- after all, it could change). That is, they don't want to 
> depend on the implicit behavior of tagged types -- or perhaps they don't 
> even know about it. Which leads to the problem that occurs here, as 
> "aliased" has slightly different meanings for functions (now just composite 
> functions) and procedures.

The original code, from the Alire project, had (I've edited it slightly)

   package Holders
   is new Ada.Containers.Indefinite_Holders (Node'Class);

   type Tree is
     new Holders.Holder
     and ...

   function Root (This : Tree) return Node'Class is
     (This.Constant_Reference);

where that Constant_Reference is inherited (eventually) from
Ada.Containers.Indefinite_Holders.Holder,

   function Constant_Reference
     (Container : aliased Holder) return Constant_Reference_Type;
   pragma Inline (Constant_Reference);

Shame it had to be there.

I've just tried splattering 'aliased' wherever the compiler told me it
was needed; it's now spreading into other packages. Ugh.

The solution might just be using composition rather than inheritance.