Re: [boost] [Units] Review

From: Matthias Schabel (boost_at_[hidden])
Date: 2007-04-03 13:14:10

> This library satisfies all of the requirements I have for a unit  
> system:
> compile-time dimensional analysis, zero runtime overhead (at least in
> theory), and explicit conversions to other systems (such as meters ->
> inches).  I recommend that this library be accepted.

Thanks for the thumbs-up.

> The only complaint I have is that unique values of ordinal<N> have  
> to be
> used.  It seems like this could cause incompatibility issues if two

Unfortunately, as Steven points out, the only other way to do this is  
ugly and convoluted unless some C++ mega-guru comes up with a way of  
generating a unique ordinal sequence of integers at compile time. I  
think that it will be impossible given the compile/link structure of C 
++ compilation, though...

> typedef for a new type, such as molar_energy_type, was something like:
>    composite_dimension<energy_type,1, amount_type,-1>::type
> instead of:
>    composite_dimension<length_tag,2, mass_tag,1, time_tag,-2,
> amount_tag,-1>::type

We're going to be going through some of the lower level code for  
defining units/systems with an eye to significantly simplifying it.  
I'll think about this at that time...

> My final suggestion is that CODATA constants should be available for
> libraries that do not support typeof.  (I expect that this will be
> fairly straightforward since the units are known.)

Right now it's implemented with Boost.Typeof - is there a compiler  
out there that is in common use that does not support typeof  
emulation at least?

Cheers, and thanks for helping out with the testing.

Matthias