Well I finally managed to string enough neurons together to write
// Specialization of autoprefix_norm for boost::units::measurement<Y> // See io.hpp // This is required to get autoprefix to work with this class. template<class Y> typename autoprefix_norm_impl<boost::units::measurement<Y>, true>::type autoprefix_norm(const boost::units::measurement<Y> & arg) { return autoprefix_norm_impl<Y, true>::call(arg); }
and that does the trick :-))
Hold on a second, doesn't that just tell Units to treat all T's as if they're double? Or is the type measurement your type? In any case autoprefix_norm_impl<T, true>::type appears to be always double, what happens if the UDT can't fit in a double? There's also a distinct lack of documentation on this, this page: http://www.boost.org/doc/libs/1_50_0/doc/html/boost_units/Reference.html mentions autoprefix_norm, but doesn't say what an overload should actually do :-(
quantity<length, measurement<double> > biglen(measurement<double>(12345.0,123.0)*meters); autoscaled = 12.345(+/-0.123) km
so many thanks.
But I'm still not clear when I could need the non-narrowing conversion in Boost.units quantity.hpp.
Nor me, there's no docs on this at all. I think it would help a great deal if the Units guys could chime in here and/or and a section on using Units with UDT's. John.