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From: ohk@tfdt-o.nta.no (Ole-Hjalmar Kristensen FOU.TD/DELAB)
Subject: Re: Ada vs C++ (Ada 0X)
Date: 1997/09/10
Message-ID: <umqpvqh5rww.fsf@fabula4-atm.nta.no>#1/1
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Organization: Telenor Online Public Access
Newsgroups: comp.lang.ada
Date: 1997-09-10T00:00:00+00:00
List-Id: <comp.lang.ada>


"James B. White, III (Trey)" <trey@osc.edu> writes:

> 
> 
> Brian Rogoff wrote:
> > I think it is obvious that you can't do this stuff with Ada generics
> > because Ada generic instantiation is not primitive recursive function
> > calculation (what a mouthful, was that clear?). 
> 
> Clear. More about this below.
> 
> > Lisp macros can do
> > arbitrary computation during expansion, so given a decent Lisp compiler
> > you should be able to get the same effect. Ask nicely on the Lisp newsgroup
> > and I bet you'll even get code.
> 
> Finding code is easy. The trick is finding a decent Lisp compiler!
> 
> > My question is whether it is necessary for your purposes to have this
> > capability directly supported in the language, or if some source to source
> > transformation tool would suffice; i.e., an Ada aware macro system or some
> > other such tool. I recall reading about such a macro system (M5?) but I
> > forget where...
> 
> If it's supported in the language, it is portable. Before anyone starts
> slamming the portability of C++ and templates, realize the situation has
> changed dramatically over the last few months.
> 

Don't bet on that. We still have template classes which are legal C++,
but which in practice can only be compiled by CenterLine CC (and
probably other Cfront derivates), but not by g++, and not by Sun CC,
because of different strategies for instantiating the templates.

> > (In case anyone missed it, the C++ techniques being discussed can be found
> >  at http://monet.uwaterloo.ca/blitz/ )
> 
> I guess my real point is the following. Expression templates in C++
> demonstrate a level of functionality absent from Ada. If the Ada
> standard is updated again (Ada 0X?), perhaps the Ada community should
> consider ways of including the capabilities of expression templates (and
> template metaprograms) in the new standard. I certainly don't advocate
> supporting C++-style templates. What I would like to see is the
> *capabilities* of these techniques added to Ada, but with a better
> implementation.
> -- 
> James B. White, III (Trey)
> Ohio Supercomputer Center
> trey@osc.edu
> <http://www.osc.edu/~trey/>
> Phone: (614)292-9291  Fax: (614)292-7168