From: Steven Watanabe (steven_at_[hidden])
Date: 2007-03-28 19:20:24
Lewis Hyatt <lhyatt <at> princeton.edu> writes:
> -What is your evaluation of the design?
> I do disagree with previous comments on the evilness of the mutating
> value() method.
We were going to replace it with
This make the fact that it is dangerous
more obvious in addition to allowing
> Also, quantity<> should pass through operator++ and operator-- in
> addition to the other arithmetic operators.
> I was surprised by the following behavior:
> #include <iostream>
> #include <boost/units/io.hpp>
> #include <boost/units/systems/si.hpp>
> #include <boost/units/systems/cgs.hpp>
> #include <boost/units/systems/si/prefixes.hpp>
> using namespace boost::units;
> int main()
> quantity<CGS::force> F0 = 20 * CGS::dyne;
> quantity<SI::force> F1 = quantity_cast<SI::force>(F0);
> quantity<SI::force> F2 = quantity_cast<SI::force>(20 * CGS::dyne);
> quantity<SI::force> F3(F0);
> //quantity<SI::force> F4 = F0;
This requires a conversion. The construtor is explicit.
> //quantity<SI::force> F5(20 * CGS::dyne);
Ouch. I noticed this before but never fixed it.
I'll take care of it immidiately
> //quantity<SI::force> F6 = 20 * CGS::dyne;
Again, the constructor is explicit.
> Also problematic is F2, which does compile, albeit with a warning, but
> then does the wrong thing at run time. The output of this program is:
> 1e-05 m kg s^(-2)
> 0 m kg s^(-2)
> 1e-05 m kg s^(-2)
> This appears to be related to the fact that in the initialization of F0,
> there is an implicit conversion from the int (20) to double.
I'll fix it.
> -What is your evaluation of the documentation?
> The large number of examples is excellent. The documentation needs a
> lot more substance to it, particularly explaining surprising features of
> implicit conversions.
Better: fix the problems.
> -What is your evaluation of the potential usefulness of the library?
> One concern I have, is that I use a lot of C++ wrappers
> over legacy C libraries such as CLAPACK and ATLAS.
If you are doing that I would put the
assertion at the point where you cast.
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