[Boost-bugs] [Boost C++ Libraries] #7138: Output of a UDT with autoprefix requires specialization of auto_prefix_norm

Subject: [Boost-bugs] [Boost C++ Libraries] #7138: Output of a UDT with autoprefix requires specialization of auto_prefix_norm
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-07-16 08:42:29

#7138: Output of a UDT with autoprefix  requires specialization of
auto_prefix_norm
----------------------------------+-----------------------------------------
 Reporter:  pbristow              |       Owner:  steven_watanabe
     Type:  Bugs                  |      Status:  new            
Milestone:  Boost 1.51.0          |   Component:  units          
  Version:  Boost 1.51.0          |    Severity:  Problem        
 Keywords:  units autoprefix UDT  |  
----------------------------------+-----------------------------------------
 Output of a UDT with autoprefix  requires specialization of
 auto_prefix_norm for the scaling to take place.  For example, to get
 expected scaling to kilometers from

 quantity<length, measurement<double> >
 biglen(measurement<double>(12345.0,123.0)*meters); autoscaled =
 12.345(+/-0.123) km

 This can be achieved by adding this to measurement.hpp (where Y is the
 type of UDT)


 {{{
 // Specialization of autoprefix_norm for UDTboost::units::measurement<Y>
 // See io.hpp.
 // This specialization 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);
 }
 }}}
 However this assumes that the class Y is convertible to double.
 autoprefix_norm_impl<T, true>::type appears to be always double.
 I am unclear if this is checked or is the responsibility or the user?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7138>
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