boost/units/static_constant.hpp

   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) 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 #ifndef BOOST_UNITS_STATIC_CONSTANT_HPP
  12 #define BOOST_UNITS_STATIC_CONSTANT_HPP
  13
  14 #include <boost/units/config.hpp>
  15
  16 /// A convenience macro that allows definition of static
  17 /// constants in headers in an ODR-safe way.
  18 #define BOOST_UNITS_STATIC_CONSTANT(name, type)             \
  19 template<bool b>                                            \
  20 struct name##_instance_t                                    \
  21 {                                                           \
  22     static const type instance;                             \
  23 };                                                          \
  24                                                             \
  25 namespace                                                   \
  26 {                                                           \
  27     static const type& name = name##_instance_t<true>::instance;   \
  28 }                                                           \
  29                                                             \
  30 template<bool b>                                            \
  31 const type name##_instance_t<b>::instance
  32
  33 /// A convenience macro for static constants with auto
  34 /// type deduction.
  35 #if BOOST_UNITS_HAS_TYPEOF
  36
  37 #if BOOST_UNITS_HAS_BOOST_TYPEOF
  38
  39 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value)               \
  40 BOOST_TYPEOF_NESTED_TYPEDEF(name##_nested_t, value)                 \
  41 BOOST_UNITS_STATIC_CONSTANT(name, name##_nested_t::type) = (value)
  42
  43 #elif BOOST_UNITS_HAS_MWERKS_TYPEOF
  44
  45 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value)               \
  46 BOOST_UNITS_STATIC_CONSTANT(name, __typeof__(value)) = (value)
  47
  48 #elif BOOST_UNITS_HAS_GNU_TYPEOF
  49
  50 #define BOOST_UNITS_AUTO_STATIC_CONSTANT(name, value)               \
  51 BOOST_UNITS_STATIC_CONSTANT(name, typeof(value)) = (value)
  52
  53 #endif // BOOST_UNITS_HAS_BOOST_TYPEOF
  54
  55 #endif // BOOST_UNITS_HAS_TYPEOF
  56
  57 #endif // BOOST_UNITS_STATIC_CONSTANT_HPP