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1 // Boost.Units - A C++ library for zero-overhead dimensional analysis and
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2 // unit/quantity manipulation and conversion
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3 //
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4 // Copyright (C) 2003-2008 Matthias Christian Schabel
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5 // Copyright (C) 2008 Steven Watanabe
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6 //
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7 // Distributed under the Boost Software License, Version 1.0. (See
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8 // accompanying file LICENSE_1_0.txt or copy at
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9 // http://www.boost.org/LICENSE_1_0.txt)
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10
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11 #ifndef BOOST_UNITS_STATIC_CONSTANT_HPP
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12 #define BOOST_UNITS_STATIC_CONSTANT_HPP
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13
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14 #include <boost/units/config.hpp>
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15
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16 /// A convenience macro that allows definition of static
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17 /// constants in headers in an ODR-safe way.
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18 #define BOOST_UNITS_STATIC_CONSTANT(name, type) \
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19 template<bool b> \
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20 struct name##_instance_t \
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21 { \
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22 static const type instance; \
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23 }; \
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24 \
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25 namespace \
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26 { \
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27 static const type& name = name##_instance_t<true>::instance; \
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28 } \
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29 \
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30 template<bool b> \
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31 const type name##_instance_t<b>::instance
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32
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33 /// A convenience macro for static constants with auto
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34 /// type deduction.
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35 #if BOOST_UNITS_HAS_TYPEOF
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36
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37 #if BOOST_UNITS_HAS_BOOST_TYPEOF
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38
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39 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value) \
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40 BOOST_TYPEOF_NESTED_TYPEDEF(name##_nested_t, value) \
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41 BOOST_UNITS_STATIC_CONSTANT(name, name##_nested_t::type) = (value)
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42
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43 #elif BOOST_UNITS_HAS_MWERKS_TYPEOF
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44
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45 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value) \
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46 BOOST_UNITS_STATIC_CONSTANT(name, __typeof__(value)) = (value)
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47
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48 #elif BOOST_UNITS_HAS_GNU_TYPEOF
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49
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50 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value) \
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51 BOOST_UNITS_STATIC_CONSTANT(name, typeof(value)) = (value)
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52
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53 #endif // BOOST_UNITS_HAS_BOOST_TYPEOF
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54
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55 #endif // BOOST_UNITS_HAS_TYPEOF
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56
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57 #endif // BOOST_UNITS_STATIC_CONSTANT_HPP
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