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+// 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 Derived*
+ check_double_register(const units::base_unit_ordinal<N>&)
+ { return(0); }
+
+ /// Register this ordinal
+ /// INTERNAL ONLY
+ friend detail::yes
+ boost_units_unit_is_registered(const units::base_unit_ordinal<N>&)
+ { detail::yes result; return(result); }
+
+ /// But make sure we can identify the current instantiation!
+ /// INTERNAL ONLY
+ friend detail::yes
+ boost_units_unit_is_registered(const units::base_unit_pair<Derived, N>&)
+ { detail::yes result; return(result); }
+};
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_BASE_UNIT_HPP