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 26 namespace boost { 27 28 namespace units { 29 30 /// This must be in namespace boost::units so that ADL 31 /// will work with friend functions defined inline. 32 /// INTERNAL ONLY 33 template<long N> struct base_dimension_ordinal { }; 34 35 /// INTERNAL ONLY 36 template<class T, long N> struct base_dimension_pair { }; 37 38 /// INTERNAL ONLY 39 template<class T, long N> 40 struct 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. 55 template<class Derived, 56 long N 57 #if !defined(BOOST_UNITS_DOXYGEN) && !defined(__BORLANDC__) 58 , 59 class = typename detail::ordinal_has_already_been_defined< 60 check_base_dimension<Derived, N>::value 61 >::type 62 #endif 63 > 64 class 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 Derived* check_double_register(const units::base_dimension_ordinal<N> &)87 check_double_register(const units::base_dimension_ordinal<N>&) 88 { return(0); } 89 90 /// Register this ordinal 91 /// INTERNAL ONLY 92 friend detail::yes boost_units_is_registered(const units::base_dimension_ordinal<N> &)93 boost_units_is_registered(const units::base_dimension_ordinal<N>&) 94 { detail::yes result; return(result); } 95 96 /// But make sure we can identify the current instantiation! 97 /// INTERNAL ONLY 98 friend detail::yes boost_units_is_registered(const units::base_dimension_pair<Derived,N> &)99 boost_units_is_registered(const units::base_dimension_pair<Derived, N>&) 100 { detail::yes result; return(result); } 101 }; 102 103 } // namespace units 104 105 } // namespace boost 106 107 #endif // BOOST_UNITS_BASE_DIMENSION_HPP 108