Re: [Boost-users] [units] easier scaled units generation

Subject: Re: [Boost-users] [units] easier scaled units generation
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-05-04 07:24:47

> While it is not (yet) standards compliant, most current C++ compilers support this,
> which is about as easy as you can get :
>
> typedef typeof(si::giga*si::pascals)    gigapascal_type;
>

ok, that is useful, I ended up doing this

namespace si{
template<class Unit> struct femto_scaled{typedef typename
make_scaled_unit<Unit, scale<10, static_rational<-15> > >::type
unit;};
template<class Unit> struct pico_scaled {typedef typename
make_scaled_unit<Unit, scale<10, static_rational<-12> > >::type
unit;};
template<class Unit> struct nano_scaled {typedef typename
make_scaled_unit<Unit, scale<10, static_rational< -9> > >::type
unit;};
template<class Unit> struct mega_scaled {typedef typename
make_scaled_unit<Unit, scale<10, static_rational< +6> > >::type
unit;};
template<class Unit> struct giga_scaled {typedef typename
make_scaled_unit<Unit, scale<10, static_rational< +9> > >::type
unit;};
//name "femto" instead of "femto_scaled" would clash with si::femto
constant
}

which works pretty well, for example

        quantity<si::femto_scaled<si::time>::unit>
one_fs(1.*si::femto*si::second);
        quantity<si::femto_scaled<si::time>::unit> one_s(1.*si::second);

        quantity<si::nano_scaled<atomic::energy>::unit>
one_nanohartree(1.*si::nano*atomic::hartree);
        quantity<si::nano_scaled<atomic::energy>::unit>
one_hartree(1.*atomic::hartree);

BUT for some strange reason doesn't completely work for this unit
(electronvolt) defined outside a system:

        quantity<si::mega_scaled<atomic::electron_volt_unit>::unit>
one_Mev(1.*si::mega*atomic::eV); //works
        quantity<si::mega_scaled<atomic::electron_volt_unit>::unit>
one_ev(1.*atomic::eV); //does not compile

electron_volt is defined as

namespace atomic{
        struct electron_volt_base_unit : base_unit<electron_volt_base_unit,
energy_dimension, 43289> {
                static const std::string name()   { return "electronvolt";}
                static const std::string symbol() { return "eV"; }
        };
        typedef electron_volt_base_unit::unit_type electron_volt_unit;
        static const electron_volt_unit electron_volt, eV;
        inline std::string symbol_string(const
reduce_unit<electron_volt_unit>::type&){return "eV";}
}
BOOST_UNITS_DEFINE_CONVERSION_FACTOR(
        boost::units::atomic::electron_volt_base_unit,
        boost::units::atomic::energy,
        double, 0.03674932
);
BOOST_UNITS_DEFAULT_CONVERSION(
        boost::units::atomic::electron_volt_base_unit,
        boost::units::atomic::energy
);

and the compiler error is

In file included from /usr/include/boost/units/
heterogeneous_system.hpp:36,
                 from /usr/include/boost/units/base_unit.hpp:15,
                 from .atomic.hpp.cpp.cpp:14:
/usr/include/boost/units/detail/linear_algebra.hpp: In instantiation
of
‘boost::units::detail::determine_extra_equations_skip_zeros_impl<true,
false>::apply<boost::units::list<boost::units::list<boost::units::static_rational<0l,
1l>, boost::units::list<boost::units::static_rational<0l, 1l>,
boost::units::dimensionless_type> >,
boost::units::dimensionless_type>, 1, 1, 3,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> > >’:
/usr/include/boost/units/detail/linear_algebra.hpp:264:   instantiated
from ‘boost::units::detail::determine_extra_equations<2,
false>::apply<boost::units::list<boost::units::list<boost::units::static_rational<0l,
1l>, boost::units::list<boost::units::static_rational<0l, 1l>,
boost::units::dimensionless_type> >,
boost::units::dimensionless_type>, 3,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> > >’
/usr/include/boost/units/detail/linear_algebra.hpp:264:   instantiated
from ‘boost::units::detail::determine_extra_equations<3,
false>::apply<boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> >, 3,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> > >’
/usr/include/boost/units/detail/linear_algebra.hpp:538:   instantiated
from
‘boost::units::detail::make_square_and_invert<boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::list<boost::units::list<boost::units::static_rational<2l,
1l>, boost::units::list<boost::units::static_rational<1l, 1l>,
boost::units::list<boost::units::static_rational<-0x00000000000000002l,
1l>, boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> > >’
/usr/include/boost/units/detail/linear_algebra.hpp:828:   instantiated
from
‘boost::units::detail::normalize_units<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> > >’
/usr/include/boost/units/detail/linear_algebra.hpp:1035:
instantiated from
‘boost::units::detail::calculate_base_unit_exponents_impl<false>::apply<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> >,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > > >’
/usr/include/boost/units/detail/linear_algebra.hpp:1051:
instantiated from
‘boost::units::detail::calculate_base_unit_exponents<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> >,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > > >’
/usr/include/boost/units/heterogeneous_system.hpp:240:   instantiated
from
‘boost::units::detail::make_heterogeneous_system<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::homogeneous_system<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> > > >’
/usr/include/boost/units/unit.hpp:93:   instantiated from
‘boost::units::reduce_unit<boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::homogeneous_system<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> > >, void> >’
/usr/include/boost/units/detail/conversion_impl.hpp:314:
instantiated from
‘boost::units::detail::conversion_impl<1>::apply<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::homogeneous_system<boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::list<boost::units::atomic::electron_volt_base_unit,
boost::units::dimensionless_type> > > >’
/usr/include/boost/units/detail/conversion_impl.hpp:445:
instantiated from
‘boost::units::detail::conversion_factor_helper<boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> >, void>,
boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::list<boost::units::scale_list_dim<boost::units::scale<10l,
boost::units::static_rational<6l, 1l> > >,
boost::units::dimensionless_type> > >, void> >’
/usr/include/boost/units/detail/conversion_impl.hpp:345:
instantiated from ‘static boost::units::quantity<Unit2, T2>
boost::units::conversion_helper<boost::units::quantity<Unit1, T1>,
boost::units::quantity<Unit2, T2> >::convert(const
boost::units::quantity<Unit1, T1>&) [with Unit1 =
boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> >, void>, T1 = double, Unit2 =
boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::list<boost::units::scale_list_dim<boost::units::scale<10l,
boost::units::static_rational<6l, 1l> > >,
boost::units::dimensionless_type> > >, void>, T2 = double]’
/usr/include/boost/units/quantity.hpp:193:   instantiated from
‘boost::units::quantity<Unit, Y>::quantity(const
boost::units::quantity<Unit2, YY>&, typename
boost::disable_if<boost::mpl::and_<typename
boost::units::is_implicitly_convertible<Unit2, Unit>::type,
boost::units::detail::is_non_narrowing_conversion<YY, Y>,
mpl_::bool_<true>, mpl_::bool_<true>, mpl_::bool_<true> >, typename
boost::units::detail::disable_if_is_same<Unit, Unit2>::type>::type*)
[with Unit2 =
boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::dimensionless_type> >, void>, YY = double, Unit =
boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::heterogeneous_system<boost::units::heterogeneous_system_impl<boost::units::list<boost::units::heterogeneous_system_dim<boost::units::atomic::electron_volt_base_unit,
boost::units::static_rational<1l, 1l> >,
boost::units::dimensionless_type>,
boost::units::list<boost::units::dim<boost::units::length_base_dimension,
boost::units::static_rational<2l, 1l> >,
boost::units::list<boost::units::dim<boost::units::mass_base_dimension,
boost::units::static_rational<1l, 1l> >,
boost::units::list<boost::units::dim<boost::units::time_base_dimension,
boost::units::static_rational<-0x00000000000000002l, 1l> >,
boost::units::dimensionless_type> > >,
boost::units::list<boost::units::scale_list_dim<boost::units::scale<10l,
boost::units::static_rational<6l, 1l> > >,
boost::units::dimensionless_type> > >, void>, Y = double]’
.atomic.hpp.cpp.cpp:416:   instantiated from here
/usr/include/boost/units/detail/linear_algebra.hpp:197: error: no type
named ‘item’ in ‘struct boost::units::dimensionless_type’
compilation terminated due to -Wfatal-errors.