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Newsgroups: comp.lang.ada
Date: Sun, 15 Jul 2018 08:33:02 -0700 (PDT)
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Subject: Re: Visibility of Indexing aspects
From: Jere <jhb.chat@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:53827
Date: 2018-07-15T08:33:02-07:00
List-Id: <comp.lang.ada>

On Sunday, July 15, 2018 at 10:41:50 AM UTC-4, AdaMagica wrote:
> Am Samstag, 14. Juli 2018 16:18:38 UTC+2 schrieb Jere:
> > Reference example compiled in GCC 8.1:
> > 
> > with Ada.Text_IO; use Ada.Text_IO;
> > 
> > procedure jdoodle is
> >     package Containers is
> > 
> >       type Container is private;
> >       
> >     private
> > 
> >       type Container_Array is array(1..20) of aliased Integer;
> >       type Container is tagged record
> >          Data : Container_Array := (others => 0);
> >       end record
> >         with Variable_Indexing => Reference;
> >       
> >       type Reference_Holder
> >          (Element : not null access Integer)
> >       is limited null record
> >          with Implicit_Dereference => Element;
> >       
> >       function Reference
> >          (Self  : aliased in out Container;
> >           Index : Positive)
> >           return Reference_Holder
> >       is (Element => Self.Data(Index)'Access);
> >       
> >     end Containers;
> >    
> >     C : aliased Containers.Container;
> > begin
> >     for Index in 1 .. 20 loop
> >         C(Index) := Index;
> >         Put_Line(Integer'Image(C(Index)));
> >     end loop;
> > end jdoodle;
> 
> Where did you get this code from? It's a plain compiler bug. How can a client know the index range?

That's why I started with my original question.  It seems very
odd that it should even be legal.  My intuition screamed bug,
but I couldn't find anything in the RM to say it was illegal.
Is there at least a statement somewhere that specifies the
legality?  I'd rather not go on just what I consider common
sense or my own intuition.

I made the example based off of someone's Ada library on github.