[Boost-bugs] [Boost C++ Libraries] #6872: units/io.hpp: autoprefix_norm_impl<> should resolve to no-op for unsigned built-in types

Subject: [Boost-bugs] [Boost C++ Libraries] #6872: units/io.hpp: autoprefix_norm_impl<> should resolve to no-op for unsigned built-in types
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-05-06 15:37:53

#6872: units/io.hpp: autoprefix_norm_impl<> should resolve to no-op for unsigned
built-in types
------------------------------------------------------+---------------------
 Reporter:  Vassilii Khachaturov <vkh@…>              |       Owner:  matthiasschabel
     Type:  Bugs                                      |      Status:  new            
Milestone:  To Be Determined                          |   Component:  units          
  Version:  Boost Development Trunk                   |    Severity:  Problem        
 Keywords:                                            |  
------------------------------------------------------+---------------------
 The code
         using namespace boost::units;
         const quantity<si::length, int> boa = 5 * si::meters;
         std::cout << boa << std::endl;
 prints "5 m", as expected, yet
         using namespace boost::units;
         const quantity<si::length, unsigned int> boa = 5 * si::meters;
         std::cout << boa << std::endl;
 fails to compile due to the std::abs call being ambiguous in io.hpp:
 template<class T>
 struct autoprefix_norm_impl<T, true>
 {
     typedef double type;
     static double call(const T& arg) { return std::abs(arg); }
 };

 There should be a specialization resolving to a no-op (just return the
 arg) for unsigned types.

 A (probably slightly heavier) user-side workaround possible one can use is
 to forcibly define the missing std::abs to be a no-op as follows:

 namespace std {
     template<typename Unsigned>
     typename boost::enable_if<boost::is_unsigned<Unsigned>,
 Unsigned>::type
         abs(const Unsigned& x)
     {
         return x; // unsigned type...
     }
 }

 Alternatively, boost::units should do a static assert that the type
 underlying the quantity is signed if that is what is intended (but why
 restrict it thus?)

 Found and tested the workaround on 1.47.0, but confirmed to still exist on
 the trunk.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6872>
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