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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Bug in Ada (SuSe 10.2) ?
Date: Wed, 27 Feb 2008 18:30:34 -0600
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Date: 2008-02-27T18:30:34-06:00
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"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
news:wcc7igq2ssj.fsf@shell01.TheWorld.com...
> billjones6789@yahoo.com writes:
...
> > Yes, here's another copy.  Randy reports a compile-time
> > error message, and Bob Klungle reports that the program
> > runs without raising program_error.
>
> Ah, thanks for reposting that.
>
> Unless I'm missing something, both compiler behaviors are bugs,
> and should be reported.  I would expect a run-time error in WoW,
> and there's no compiler switch that's supposed to turn this
> check on -- it's supposed to be on by default.

Why do you think a compile-time message is a bug? I've convinced myself that
it is correct. Look at the body of WoW closely:

    function WoW (Slats: access AirSpeed) return Int_Access is
    begin
         return Slats.Altitude'Access;
    end WoW;

Since Slats is an access value, this is really a dereference. That is, the
return statement really is:

         return Slats.all.Altitude'Access;

And you lose the special (dynamic) accessibility with the dereference. Thus,
you get a static check (which fails in this case).

                                       Randy.






> > with Ada.Text_IO;
> > procedure Dangling_Pointer2 is
> >    type Int_Access is access all integer;
> >
> >    Save : Int_Access;
> >
> >    type AirSpeed is record
> >       Altitude : aliased integer := 9;
> >    end record;
> >
> >    function WoW (Slats: access AirSpeed) return Int_Access is
> >    begin
> >       return Slats.Altitude'Access;
> >    end WoW;
> >
> >    procedure Calculate is
> >       Heading : aliased AirSpeed;
> >    begin
> >       Save := WoW (Heading'access);
> >       Ada.Text_IO.Put_Line (integer'image(Save.all));
> >    end Calculate;
> >
> >    procedure Mess_with_stack is
> >       Dummy: array(1..10) of integer := (others => 17);
> >    begin
> >       null;
> >    end Mess_with_stack;
> >
> > begin
> >    Calculate;
> >    Mess_with_stack;
> >    Ada.Text_IO.Put_Line (integer'image(Save.all));
> > end Dangling_Pointer2;
>
> - Bob