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 dimensions (mass, length, time...).
13/// \details base dimension definition registration.
14
15#ifndef BOOST_UNITS_BASE_DIMENSION_HPP
16#define BOOST_UNITS_BASE_DIMENSION_HPP
17
18#include <boost/units/config.hpp>
19#include <boost/units/dim.hpp>
20#include <boost/units/static_rational.hpp>
21#include <boost/units/units_fwd.hpp>
22#include <boost/units/detail/dimension_list.hpp>
23#include <boost/units/detail/ordinal.hpp>
24#include <boost/units/detail/prevent_redefinition.hpp>
25
26namespace boost {
27
28namespace units {
29
30/// This must be in namespace boost::units so that ADL
31/// will work with friend functions defined inline.
32/// INTERNAL ONLY
33template<long N> struct base_dimension_ordinal { };
34
35/// INTERNAL ONLY
36template<class T, long N> struct base_dimension_pair { };
37
38/// INTERNAL ONLY
39template<class T, long N>
40struct check_base_dimension {
41 enum {
42 value =
43 sizeof(boost_units_is_registered(units::base_dimension_ordinal<N>())) == sizeof(detail::yes) &&
44 sizeof(boost_units_is_registered(units::base_dimension_pair<T, N>())) != sizeof(detail::yes)
45 };
46};
47
48/// Defines a base dimension. To define a dimension you need to provide
49/// the derived class (CRTP) and a unique integer.
50/// @code
51/// struct my_dimension : boost::units::base_dimension<my_dimension, 1> {};
52/// @endcode
53/// It is designed so that you will get an error message if you try
54/// to use the same value in multiple definitions.
55template<class Derived,
56 long N
57#if !defined(BOOST_UNITS_DOXYGEN) && !defined(BOOST_BORLANDC)
58 ,
59 class = typename detail::ordinal_has_already_been_defined<
60 check_base_dimension<Derived, N>::value
61 >::type
62#endif
63>
64class base_dimension :
65 public ordinal<N>
66{
67 public:
68 /// INTERNAL ONLY
69 typedef base_dimension this_type;
70 /// A convenience typedef. Equivalent to boost::units::derived_dimension<Derived,1>::type.
71#ifndef BOOST_UNITS_DOXYGEN
72 typedef list<dim<Derived,static_rational<1> >, dimensionless_type> dimension_type;
73#else
74 typedef detail::unspecified dimension_type;
75#endif
76 /// Provided for mpl compatability.
77 typedef Derived type;
78
79 private:
80 /// Check for C++0x. In C++0x, we have to have identical
81 /// arguments but a different return type to trigger an
82 /// error. Note that this is only needed for clang as
83 /// check_base_dimension will trigger an error earlier
84 /// for compilers with less strict name lookup.
85 /// INTERNAL ONLY
86 friend BOOST_CONSTEXPR Derived*
87 check_double_register(const units::base_dimension_ordinal<N>&)
88 { return(0); }
89
90 /// Register this ordinal
91 /// INTERNAL ONLY
92 friend BOOST_CONSTEXPR detail::yes
93 boost_units_is_registered(const units::base_dimension_ordinal<N>&)
94 { return(detail::yes()); }
95
96 /// But make sure we can identify the current instantiation!
97 /// INTERNAL ONLY
98 friend BOOST_CONSTEXPR detail::yes
99 boost_units_is_registered(const units::base_dimension_pair<Derived, N>&)
100 { return(detail::yes()); }
101};
102
103} // namespace units
104
105} // namespace boost
106
107#endif // BOOST_UNITS_BASE_DIMENSION_HPP
108

source code of boost/libs/units/include/boost/units/base_dimension.hpp