Re: [boost] Boost Units library preview

From: Andy Little (andy_at_[hidden])
Date: 2006-08-26 08:03:13

"Matthias Troyer" <troyer_at_[hidden]> wrote in message 
news:2F9215A5-A36E-4139-A289-E0E6C095AEC5_at_itp.phys.ethz.ch...
>
> On Aug 23, 2006, at 8:50 PM, Andy Little wrote:
>
>>
>> This is merely because the use cases are potentially  pretty wide.
>> In the review
>> I made it clear that I was limiting the scope of Quan to the SI
>> unit system,
>> because that is the one I understand. If I resubmitted the library
>> it could be
>> rejected as not being generic enough and  there are inklings from
>> this thread
>> that this may be the reaction. But I don't have the time or the
>> knowledge to
>> write a truly generic physical quantities library and if that is
>> the requirement
>> then there isnt much point in resubmitting Quan for another review
>> AFAICS.
>
> Can the dimension checking part of the library be used without the SI
> unit system? For most other unit systems I use, I mainly need
> dimension checking and not conversions between different units, such
> as km or m? Thus just a quantity with dimensions would be useful to
> catch programming errors.

Yes.  In the signature fixed_quantity<Unit, ValueType>, the Unit parameter can 
be so modelled that it only allows base units to be used, and in this case there 
is no conversion overhead BTW, a multiply is simply a multiply of the numeric 
values for example).  By default Quan wont work across Unit models (IOW the 
class template names of units must match), which means that attempting to do 
calculations between Units with different class template names will fail at 
compile time. By this means you can guarantee that you can prevent any 
conversions. (FWIW there is also the option to allow  unit conversions but make 
them explicit, prompted by Deane Yang easrlier in this thread.)

As yet this only applies easily to the CVS version of Quan, but I hope that we 
will be able to get another release out shortly, which reflects what is 
currently in the CVS version.  I will hopefully announce it boost.devel once the 
next release is available.

regards
Andy Little