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From: Matthias Schabel (boost_at_[hidden])
Date: 2003-11-18 18:29:59

> Hi Matt I have had a look at your code and compiled on VC7.1 MSos with
> a
> couple of mods.

Cool - that's good news. Metrowerks pukes on it; a little too much
MPL, I guess.
I'm still mystified by the asymmetry between the normal and assignment
forms of the
constructor (commented out in test_units.cpp. Could you try
uncommenting those
statements in VC7.1 to see what pops out? I don't have access to that

> template<class T>
> void write_typeid()
> {
> // std::system((std::string("c++filt ")+
> // std::string(typeid(T).name())).c_str());
> std::cout << typeid(T).name()<< std::endl;
> }

Yeah, sorry about that - gcc's typeid gives the mangled class name
which is about useless
for debugging complex MPL sequences.

> As far as the rest goes, the MPL stuff looks very impressive
> and I like the removal of dimensions with power 0.
> On that subject it would be nice once having arrived at a
> dimensionless pq
> to convert to the value_type direct.
> ie ideally a dimensionless pq is never constructed

Glad you like it; some parts were a bear to get right. At the moment,
I allow dimensionless
quantities to be implicitly converted to/from the underlying value
type. I like preserving
the dimensionlessness (d15s?) so that you can distinguish between raw
values and
types which result from evaluation of expressions containing
dimensioned quantities...

> If you wrote up documentation on that I would be interested and
> comparing my stuff with yours I have to admit that most on Boost will
> probably prefer yours... because its nice and technical :-)
> but to convey what youre doing it obviously needs documentation.

At this point I feel like the dimensional analysis part is pretty much
but I'm still working on schemes for the dimensioned quantities which
maximize flexibility. In particular, I'm trying to concoct a good way
to take
two disparate models and merge them - say you have one model with
length_tag, time_tag, and mass_tag and another with angle_tag, it would
be nice to be able to easily create a meta-model encompassing both...
also interested to hear what others are looking for in such a library.

> If you do set up a working group on units/d.a./pqs whatever I would be
> interested.

Will do.

> What I am trying to achieve is best summed up in this previous post.
> Would be interesting to see how it would look with your scheme ?

I'm personally on the explicit conversion only side of the fence - the
idea of
setting up a system for intelligently determining the minimum required
for the result of an arbitrary unit-containing expression sounds like
it would be
an interesting application for expression templates, though I suspect
it will be
very difficult to accomplish for general (rather than POD) value

Matthias Schabel, Ph.D.
Utah Center for Advanced Imaging Research
729 Arapeen Drive
Salt Lake City, UT 84108
801-587-9413 (work)
801-585-3592 (fax)
801-706-5760 (cell)
801-484-0811 (home)
mschabel at ucair med utah edu

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