+ namespace range_detail
+ {
+ template<class SinglePassRange>
+ inline BOOST_DEDUCED_TYPENAME range_size<const SinglePassRange>::type
+ range_calculate_size(const SinglePassRange& rng)
+ {
+ BOOST_ASSERT( (boost::end(rng) - boost::begin(rng)) >= 0 &&
+ "reachability invariant broken!" );
+ return boost::end(rng) - boost::begin(rng);
+ }
+ }