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From: "Pat Rogers" <progers@classwide.com>
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Subject: Re: Refactoring and Ada
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"Randy Brukardt" <randy@rrsoftware.com> wrote in message
news:u78hac6o7iku15@corp.supernews.com...
> >No, I was asking for the exegesis in terms of the RM for Richard's much
> more sweeping "comdemnation" of the attribute.  ("Condemnation" is too
> strong here, but you get the idea.)
>
> Reading AI-167 might help some
> (http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00167.TXT?rev=1.5).
> But this AI is still under construction (it is not, and never has been,
> approved, contrary to the statement of someone else here), and
> undoubtably will change.
<snip>
> The problem rule is 13.9.1(12), which makes the CALL to
> Unchecked_Conversion erroneous if the result is invalid. And this rule
> is intended (I forget why, Bob?).

Thanks (again) for the pointer to the AI in progress.  Clearly there is a
problem for unchecked conversion in this case.

However, unchecked conversion isn't the only way to get the value to which
'Valid is applied.  For example, via RM 13.9.2(11):

  P : aliased Positive;

  K : Integer;
  for K'Address use P'Address;

begin
  K := 0;
  if P'Valid then ...

or, for that matter, via System.Address_To_Access_Conversions (for Integer in
this example).

The OP's saying that 'Valid is useless isn't justified by the problem with
unchecked conversion, IMHO.

What am I missing?

Pat