ceph/src/boost/boost/units/base_unit.hpp

   1 // Boost.Units - A C++ library for zero-overhead dimensional analysis and
   2 // unit/quantity manipulation and conversion
   3 //
   4 // Copyright (C) 2003-2008 Matthias Christian Schabel
   5 // Copyright (C) 2007-2008 Steven Watanabe
   6 //
   7 // Distributed under the Boost Software License, Version 1.0. (See
   8 // accompanying file LICENSE_1_0.txt or copy at
   9 // http://www.boost.org/LICENSE_1_0.txt)
  10
  11 /// \file
  12 /// \brief base unit (meter, kg, sec...).
  13 /// \details base unit definition registration.
  14
  15 #ifndef BOOST_UNITS_BASE_UNIT_HPP
  16 #define BOOST_UNITS_BASE_UNIT_HPP
  17
  18 #include <boost/units/config.hpp>
  19 #include <boost/units/heterogeneous_system.hpp>
  20 #include <boost/units/static_rational.hpp>
  21 #include <boost/units/units_fwd.hpp>
  22 #include <boost/units/unit.hpp>
  23 #include <boost/units/detail/dimension_list.hpp>
  24 #include <boost/units/detail/ordinal.hpp>
  25 #include <boost/units/detail/prevent_redefinition.hpp>
  26
  27 namespace boost {
  28
  29 namespace units {
  30
  31 /// This must be in namespace boost::units so that ADL
  32 /// will work with friend functions defined inline.
  33 /// Base dimensions and base units are independent.
  34 /// INTERNAL ONLY
  35 template<long N> struct base_unit_ordinal { };
  36
  37 /// INTERNAL ONLY
  38 template<class T, long N> struct base_unit_pair { };
  39
  40 /// INTERNAL ONLY
  41 template<class T, long N>
  42 struct check_base_unit {
  43     enum {
  44         value =
  45             sizeof(boost_units_unit_is_registered(units::base_unit_ordinal<N>())) == sizeof(detail::yes) &&
  46             sizeof(boost_units_unit_is_registered(units::base_unit_pair<T, N>())) != sizeof(detail::yes)
  47     };
  48 };
  49
  50 /// Defines a base unit.  To define a unit you need to provide
  51 /// the derived class (CRTP), a dimension list and a unique integer.
  52 /// @code
  53 /// struct my_unit : boost::units::base_unit<my_unit, length_dimension, 1> {};
  54 /// @endcode
  55 /// It is designed so that you will get an error message if you try
  56 /// to use the same value in multiple definitions.
  57 template<class Derived,
  58          class Dim,
  59          long N
  60 #if !defined(BOOST_UNITS_DOXYGEN) && !defined(__BORLANDC__)
  61          ,
  62          class = typename detail::ordinal_has_already_been_defined<
  63              check_base_unit<Derived, N>::value
  64          >::type
  65 #endif
  66 >
  67 class base_unit :
  68     public ordinal<N>
  69 {
  70     public:
  71         /// INTERNAL ONLY
  72         typedef void boost_units_is_base_unit_type;
  73         /// INTERNAL ONLY
  74         typedef base_unit           this_type;
  75         /// The dimensions of this base unit.
  76         typedef Dim                 dimension_type;
  77
  78         /// Provided for mpl compatability.
  79         typedef Derived type;
  80
  81         /// The unit corresponding to this base unit.
  82 #ifndef BOOST_UNITS_DOXYGEN
  83         typedef unit<
  84             Dim,
  85             heterogeneous_system<
  86                 heterogeneous_system_impl<
  87                     list<
  88                         heterogeneous_system_dim<Derived,static_rational<1> >,
  89                         dimensionless_type
  90                     >,
  91                     Dim,
  92                     no_scale
  93                 >
  94             >
  95         > unit_type;
  96 #else
  97         typedef detail::unspecified unit_type;
  98 #endif
  99
 100     private:
 101         /// Check for C++0x.  In C++0x, we have to have identical
 102         /// arguments but a different return type to trigger an
 103         /// error.  Note that this is only needed for clang as
 104         /// check_base_unit will trigger an error earlier
 105         /// for compilers with less strict name lookup.
 106         /// INTERNAL ONLY
 107         friend Derived*
 108         check_double_register(const units::base_unit_ordinal<N>&)
 109         { return(0); }
 110
 111         /// Register this ordinal
 112         /// INTERNAL ONLY
 113         friend detail::yes
 114         boost_units_unit_is_registered(const units::base_unit_ordinal<N>&)
 115         { detail::yes result; return(result); }
 116
 117         /// But make sure we can identify the current instantiation!
 118         /// INTERNAL ONLY
 119         friend detail::yes
 120         boost_units_unit_is_registered(const units::base_unit_pair<Derived, N>&)
 121         { detail::yes result; return(result); }
 122 };
 123
 124 } // namespace units
 125
 126 } // namespace boost
 127
 128 #endif // BOOST_UNITS_BASE_UNIT_HPP