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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Q: unboxed values and polymorphism
Date: 1996/06/22
Message-ID: <DtEHCE.34x@world.std.com>#1/1
X-Deja-AN: 161546917
references: <uvv7mt7ubgd.fsf@chaq.informatik.uni-tuebingen.de>
 <Dt4FCx.29H.0.-s@inmet.camb.inmet.com>
 <uvvwx1661tz.fsf@chaq.informatik.uni-tuebingen.de>
 <dewar.835121144@schonberg>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.ada
Date: 1996-06-22T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <dewar.835121144@schonberg>, Robert Dewar <dewar@cs.nyu.edu> wrote:
>You are encoding at a very low level, appropriate for C (since it is the
>only way to do things), but totally inappropriate for Ada. You need a
>variant record with a discriinant to indicate whether you have fixnums
>or indices. The discriminant would be a single bit.

And the pointer would be 31 bits, so the whole thing fits in 32?  Quite
reasonable, except that I've never heard of an Ada compiler that can
support that kind of packing.  Certainly, the RM does not require
support for that sort of packing.

No, I think the low-level technique used to do this in C is exactly the
same low-level technique that is necessary in Ada.  The nice thing about
Ada is that it allows you to isolate such low-level stuff from the bulk
of your application.

- Bob