boost/units/detail/dim_impl.hpp

// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
// unit/quantity manipulation and conversion
//
// Copyright (C) 2003-2008 Matthias Christian Schabel
// Copyright (C) 2008 Steven Watanabe
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_UNITS_DIM_IMPL_HPP
#define BOOST_UNITS_DIM_IMPL_HPP
#include <boost/mpl/bool.hpp>
#include <boost/mpl/less.hpp>
#include <boost/units/units_fwd.hpp>
/// \file 
/// \brief Class encapsulating a dimension tag/value pair
namespace boost {
namespace units {
namespace detail {
struct dim_tag;
}
}
namespace mpl {
/// Less than comparison for sorting @c dim.
template<>
struct less_impl<boost::units::detail::dim_tag, boost::units::detail::dim_tag>
{
    template<class T0, class T1>
    struct apply : mpl::less<typename T0::tag_type, typename T1::tag_type> {};
};
}
namespace units {
template<class Tag, class Exponent>
struct dim;
template<long N, long D>
class static_rational;
namespace detail {
/// Extract @c tag_type from a @c dim.
template<typename T>
struct get_tag
{
    typedef typename T::tag_type    type;
};
/// Extract @c value_type from a @c dim.
template<typename T>
struct get_value
{
    typedef typename T::value_type    type;
};
/// Determine if a @c dim is empty (has a zero exponent).
template<class T>
struct is_empty_dim;
template<typename T>
struct is_empty_dim< dim<T, static_rational<0, 1> > > :
    mpl::true_ 
{ };
template<typename T, typename V>
struct is_empty_dim< dim<T, V> > :
    mpl::false_ 
{ };
} // namespace detail
} // namespace units
} // namespace boost
#endif // BOOST_UNITS_DIM_IMPL_HPP