129 lines
4.1 KiB
C++
129 lines
4.1 KiB
C++
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// Boost.Units - A C++ library for zero-overhead dimensional analysis and
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// unit/quantity manipulation and conversion
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//
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// Copyright (C) 2003-2008 Matthias Christian Schabel
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// Copyright (C) 2007-2008 Steven Watanabe
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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/// \file
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/// \brief base unit (meter, kg, sec...).
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/// \details base unit definition registration.
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#ifndef BOOST_UNITS_BASE_UNIT_HPP
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#define BOOST_UNITS_BASE_UNIT_HPP
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#include <boost/units/config.hpp>
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#include <boost/units/heterogeneous_system.hpp>
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#include <boost/units/static_rational.hpp>
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#include <boost/units/units_fwd.hpp>
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#include <boost/units/unit.hpp>
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#include <boost/units/detail/dimension_list.hpp>
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#include <boost/units/detail/ordinal.hpp>
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#include <boost/units/detail/prevent_redefinition.hpp>
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namespace boost {
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namespace units {
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/// This must be in namespace boost::units so that ADL
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/// will work with friend functions defined inline.
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/// Base dimensions and base units are independent.
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/// INTERNAL ONLY
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template<long N> struct base_unit_ordinal { };
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/// INTERNAL ONLY
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template<class T, long N> struct base_unit_pair { };
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/// INTERNAL ONLY
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template<class T, long N>
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struct check_base_unit {
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enum {
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value =
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sizeof(boost_units_unit_is_registered(units::base_unit_ordinal<N>())) == sizeof(detail::yes) &&
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sizeof(boost_units_unit_is_registered(units::base_unit_pair<T, N>())) != sizeof(detail::yes)
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};
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};
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/// Defines a base unit. To define a unit you need to provide
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/// the derived class (CRTP), a dimension list and a unique integer.
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/// @code
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/// struct my_unit : boost::units::base_unit<my_unit, length_dimension, 1> {};
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/// @endcode
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/// It is designed so that you will get an error message if you try
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/// to use the same value in multiple definitions.
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template<class Derived,
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class Dim,
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long N
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#if !defined(BOOST_UNITS_DOXYGEN) && !defined(__BORLANDC__)
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,
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class = typename detail::ordinal_has_already_been_defined<
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check_base_unit<Derived, N>::value
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>::type
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#endif
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>
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class base_unit :
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public ordinal<N>
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{
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public:
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/// INTERNAL ONLY
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typedef void boost_units_is_base_unit_type;
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/// INTERNAL ONLY
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typedef base_unit this_type;
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/// The dimensions of this base unit.
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typedef Dim dimension_type;
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/// Provided for mpl compatability.
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typedef Derived type;
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/// The unit corresponding to this base unit.
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#ifndef BOOST_UNITS_DOXYGEN
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typedef unit<
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Dim,
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heterogeneous_system<
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heterogeneous_system_impl<
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list<
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heterogeneous_system_dim<Derived,static_rational<1> >,
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dimensionless_type
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>,
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Dim,
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no_scale
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>
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>
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> unit_type;
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#else
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typedef detail::unspecified unit_type;
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#endif
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private:
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/// Check for C++0x. In C++0x, we have to have identical
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/// arguments but a different return type to trigger an
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/// error. Note that this is only needed for clang as
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/// check_base_unit will trigger an error earlier
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/// for compilers with less strict name lookup.
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/// INTERNAL ONLY
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friend Derived*
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check_double_register(const units::base_unit_ordinal<N>&)
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{ return(0); }
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/// Register this ordinal
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/// INTERNAL ONLY
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friend detail::yes
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boost_units_unit_is_registered(const units::base_unit_ordinal<N>&)
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{ detail::yes result; return(result); }
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/// But make sure we can identify the current instantiation!
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/// INTERNAL ONLY
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friend detail::yes
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boost_units_unit_is_registered(const units::base_unit_pair<Derived, N>&)
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{ detail::yes result; return(result); }
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};
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} // namespace units
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} // namespace boost
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#endif // BOOST_UNITS_BASE_UNIT_HPP
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