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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Pascal Calling Convention
Date: Wed, 30 Mar 2011 08:50:13 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-03-30T08:50:13-04:00
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Adam Beneschan <adam@irvine.com> writes:

> If that feature were added, I'd want the language to specify that the
> value of the attribute must be a valid value for the subtype.

Yes.

>...(Maybe
> that's what you meant and didn't say so explicitly?)  That would still
> be a no-op if every bit pattern would be a valid value, which would be
> the case for Integer (or for the first subtype of a "mod 2**32" or
> "mod 2**64" type on most machines, which I think would be needed to
> make Hyman's example work).

Perhaps the feature would only be allowed on such (sub)types.
You'd need some way to declare such types.  "Type T is
at least 1..1_000_000, possibly larger, but make sure
all bit patterns are meaningful."  Or maybe require that
T'Base have this property for all integer types T.

I don't think you want this feature for floats and pointers.

Records and arrays?

But it's such a corner case, I doubt you really want this feature
at all!  ;-)

By the way, I invented this feature some years ago, when I read about
the data structure Hyman mentioned.  I said to myself, "That's
interesting.  I wonder how I'd design a high-level language in
which that thing could be written (correctly, and portably)."

- Bob