boost/units/base_unit.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) 2007-2008 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)
/// \file
/// \brief base unit (meter, kg, sec...).
/// \details base unit definition registration.
#ifndef BOOST_UNITS_BASE_UNIT_HPP
#define BOOST_UNITS_BASE_UNIT_HPP
#include <boost/units/config.hpp>
#include <boost/units/heterogeneous_system.hpp>
#include <boost/units/static_rational.hpp>
#include <boost/units/units_fwd.hpp>
#include <boost/units/unit.hpp>
#include <boost/units/detail/dimension_list.hpp>
#include <boost/units/detail/ordinal.hpp>
#include <boost/units/detail/prevent_redefinition.hpp>
namespace boost {
namespace units {
/// This must be in namespace boost::units so that ADL
/// will work with friend functions defined inline.
/// Base dimensions and base units are independent.
/// INTERNAL ONLY
template<long N> struct base_unit_ordinal { };
/// INTERNAL ONLY
template<class T, long N> struct base_unit_pair { };
/// INTERNAL ONLY
template<class T, long N>
struct check_base_unit {
enum {
value =
sizeof(boost_units_unit_is_registered(units::base_unit_ordinal<N>())) == sizeof(detail::yes) &&
sizeof(boost_units_unit_is_registered(units::base_unit_pair<T, N>())) != sizeof(detail::yes)
};
};
/// Defines a base unit. To define a unit you need to provide
/// the derived class (CRTP), a dimension list and a unique integer.
/// @code
/// struct my_unit : boost::units::base_unit<my_unit, length_dimension, 1> {};
/// @endcode
/// It is designed so that you will get an error message if you try
/// to use the same value in multiple definitions.
template<class Derived,
class Dim,
long N
#if !defined(BOOST_UNITS_DOXYGEN) && !defined(__BORLANDC__)
,
class = typename detail::ordinal_has_already_been_defined<
check_base_unit<Derived, N>::value
>::type
#endif
>
class base_unit :
public ordinal<N>
{
public:
/// INTERNAL ONLY
typedef void boost_units_is_base_unit_type;
/// INTERNAL ONLY
typedef base_unit this_type;
/// The dimensions of this base unit.
typedef Dim dimension_type;
/// Provided for mpl compatability.
typedef Derived type;
/// The unit corresponding to this base unit.
#ifndef BOOST_UNITS_DOXYGEN
typedef unit<
Dim,
heterogeneous_system<
heterogeneous_system_impl<
list<
heterogeneous_system_dim<Derived,static_rational<1> >,
dimensionless_type
>,
Dim,
no_scale
>
>
> unit_type;
#else
typedef detail::unspecified unit_type;
#endif
private:
/// Check for C++0x. In C++0x, we have to have identical
/// arguments but a different return type to trigger an
/// error. Note that this is only needed for clang as
/// check_base_unit will trigger an error earlier
/// for compilers with less strict name lookup.
/// INTERNAL ONLY
friend BOOST_CONSTEXPR Derived*
check_double_register(const units::base_unit_ordinal<N>&)
{ return(0); }
/// Register this ordinal
/// INTERNAL ONLY
friend BOOST_CONSTEXPR detail::yes
boost_units_unit_is_registered(const units::base_unit_ordinal<N>&)
{ return(detail::yes()); }
/// But make sure we can identify the current instantiation!
/// INTERNAL ONLY
friend BOOST_CONSTEXPR detail::yes
boost_units_unit_is_registered(const units::base_unit_pair<Derived, N>&)
{ return(detail::yes()); }
};
} // namespace units
} // namespace boost
#endif // BOOST_UNITS_BASE_UNIT_HPP