Re: [Boost-bugs] [Boost C++ Libraries] #10270: square root of boost units scaled_unit fails to compile

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #10270: square root of boost units scaled_unit fails to compile
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-01-31 00:53:20

#10270: square root of boost units scaled_unit fails to compile
-------------------------------+-----------------------------
  Reporter:  sharifmarat@…     |      Owner:  matthiasschabel
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  units
   Version:  Boost 1.55.0      |   Severity:  Problem
Resolution:                    |   Keywords:  scale
-------------------------------+-----------------------------

Comment (by Wouter Boomsma <wb@…>):

 I'm stuck with the same problem. Is there any hope for a fix in the near
 future? It would really be greatly appreciated.

 As far as I can see, the suggested work-around does not work in my case,
 since the scaled unit is not a base unit. In my application, I need a
 kilojoule unit. The obvious approach would be:
     typedef make_scaled_unit<si::energy, scale<10, static_rational<3> >
 >::type energy_unit_kJ;
 However, if this unit is involved in any nontrivial calculations involving
 sqrt or pow, it fails as described above.

 The scaled_base_unit workaround suggested by bnorman does not work
 directly since joule is not a base unit. Instead, I attempted to define a
 base unit from scratch, and set up the conversion factory manually:

 struct energy_base_unit_kJ: base_unit<energy_base_unit_kJ,
 energy_dimension, 1> {

     static std::string name() {return "kilojoule";}

     static std::string symbol() { return "kJ"; }
 };

 BOOST_UNITS_DEFINE_CONVERSION_FACTOR(
         energy_base_unit_kJ,
         si::energy,
         double, 1/1000.0);

 The problem is that I cannot define the reverse conversion factor because
 si::energy is not a base unit, and BOOST_UNITS_DEFINE_CONVERSION_FACTOR
 requires its first argument to be a base unit.

 If there is some clever way to work around this, I would appreciate a
 pointer in the right direction - but under all circumstances, it would
 really be convenient if make_scaled_unit just worked.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10270#comment:3>
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