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 |
129 | |