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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Extending A Generic Signature Package
Date: 1997/03/22
Message-ID: <E7GA75.Lnr@world.std.com>#1/1
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References: <5gkv23INN3rn@thalamus.cis.ohio-state.edu>
 <5gn90o$gm1@sutton.cs.columbia.edu> <5gtvbv$1nj@pandora.cs.utwente.nl>
 <Pine.SGI.3.95.970321164136.22672B-100000@shellx.best.com>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1997-03-22T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <Pine.SGI.3.95.970321164136.22672B-100000@shellx.best.com>,
Brian Rogoff  <bpr@best.com> wrote:
>	What if the objects are small, and there are very many of them?
>Example: your signatures are of numeric types which are the elements of 
>         matrices in a numerical linear algebra package. One or two
>         pointers per object is too much.

It's really just *one* pointer -- I don't of any implementation that
uses two, and I don't know any reason why it would want to (at least,
not as the default implementation of tagged types).  I agree that even
just one pointer is too much in the case above.

It would be nice if it were possible to implement tagged types without
storing a tag in every object.  It is *almost* possible to do that.  The
problem is that all tagged parameters are aliased, so the tag needs to
be stored.  The only way around that I can see would be to do some
global (link time) analysis of the program.

- Bob