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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Pascal Calling Convention
Date: Tue, 29 Mar 2011 14:30:59 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-03-29T14:30:59-04:00
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Hyman Rosen <hyrosen@mail.com> writes:

> And it's a good program to keep at hand to serve as a counterexample
> when programming languages want access to uninitialized data to be
> undefined behavior. It's more sensible to regard such data as having
> arbitrary but fixed values, subject to a validity check.

Just because you know of one algorithm that could use that semantics?!
(OK, I know of one other case.  Sort of.)

If I wanted to add this "feature" to Ada, I'd do so via an attribute:
T'Arbitrary_Value returns an arbitrary value of type T.  Then:

    My_Array := (1..1_000_000 => Integer'Arbitrary_Value);

can be implemented in zero machine instructions.  You really don't want
to use arbitrary values by accident.

At least with "undefined behavior", or "erroneous execution" the
compiler can have a mode that detects uninit vars at run time, which can
be useful for debugging.  GNAT has a mode that detects most uninit vars
at run time (although using uninit is no longer erroneous in Ada).

- Bob