[boost] [units] objects with internal linkage in headers

From: Steven Watanabe (steven_at_[hidden])
Date: 2007-02-12 20:28:52

AMDG

All the static const objects in the library cause ODR
violations for functions that use them.  You can avoid
this by only putting a reference in the unnamed namespace.

#define BOOST_UNITS_STATIC_CONSTANT(type, name)    \
    template<bool> struct name##_intance_t {       \
        static const type instance;                \
    };                                             \
    namespace {                                    \
        const type& name(name##_intance_t<true>::instance);\
    }                                              \
    template<bool b>                               \
    type name##_intance_t<b>::instance

BOOST_UNITS_STATIC_CONSTANT(energy, joule);
BOOST_UNITS_STATIC_CONSTANT(typeof(1.0*meters/second) , c) = 
299792458*meters/second;

In Christ,
Steven Watanabe