Re: [boost] [review] pqs

From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2006-06-09 04:00:02

----Original Message----
From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]] On Behalf Of Andy Little Sent:
08 June 2006 17:46 To: boost_at_[hidden]
Subject: Re: [boost] [review] pqs

> Although liter is equivalent to 1 dm^3, technically its not an SI
> unit. Its not in the review version of PQS, but it is possible to
> add a liter unit to volume header  and get output as
> 
> 1 L
> 
> or  whatever is preferred...  I just did this in my local version of
> PQS. 
> 
> The sequence of steps is
> 
> 1) In <boost/pqs/meta/components/of_volume.hpp>
> 
>     Add a typedef for the liter in the incoherent_unit struct (starts
> at line 47).
[SNIP]

That is not good.  Not good at all.

As far as I am concerned, a third party library file is (almost)
sacrosanct.  I would not want to edit it except to fix the most extreme
bug - what happens when I upgrade to the next version of PQS.

Can I add liter support externally to PQS?  (For example, so I can refer
to "litre").
> 
>             typedef meta::unit<
>                 boost::pqs::meta::rational<-3>,
>                  meta::rational<1>::type,
>                  boost::mpl::int_<1>
>             > liter;
> 
> 2)
> 
> In <boost/pqs/t1_quantity/types/volume.hpp>
> 
>     Add the typedef for liter to the other member typedefs:
> 
>          typedef t1_quantity<
>             type,
>             typename incoherent_unit::liter,
>             Value_type
>         > liter;
> 
> 3) In <boost/pqs/t1_quantity/types/out/volume.hpp> add the stream
> output 
> overload for the liter unit:
> 
>  inline
>     std::ostream&
>     operator <<(
>         std::ostream & os,
>         t1_quantity_units_out<
>             meta::components::of_volume::type,
>             meta::components::of_volume::incoherent_unit::liter
>         >
>     )
>     {
>         os << "L";
>         return os;
>     }
> 
> 
> Check it works:
> 
> #include <boost/pqs/t1_quantity/types/out/volume.hpp>
> using boost::pqs::volume;
> 
> int main()
> {
>    volume::liter v(1);
>    std::cout << v <<'\n';
>    volume::m3 v1 = v;
>    std::cout << v1 <<'\n';
> }
> 
> Outputs:
> 
> 1 L
> 0.001 m3
> 
> Because liter isnt an SI unit you would need to add cL and mL in the
> same way (I 
> guess that would be the next question!)
> 
> regards
> Andy Little

-- 
Martin Bonner
Martin.Bonner_at_[hidden]
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ,
ENGLAND Tel: [phone]