Boost C++ Libraries: Ticket #10270: square root of boost units scaled_unit fails to compile

bnorman@… — Tue, 29 Jul 2014 21:02:27 GMT

I'm hung up on exactly the same problem.

bnorman@… — Tue, 29 Jul 2014 22:26:03 GMT

I'm hung up on exactly the same problem.

FYI, I am now able to work around this issue as follows:

typedef scaled_base_unit<si::meter_base_unit,
                         scale<10, static_rational<-6> > >::type micro_meter_base_unit;
typedef micro_meter_base_unit::unit_type micro_meter_unit;

Sat, 31 Jan 2015 00:53:20 GMT

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.

petamas@… — Fri, 20 Mar 2015 12:14:54 GMT

Hi all, here's a fix for this problem:

namespace boost
{
  namespace mpl
  {
    template<>
    struct divides_impl<boost::units::scale_dim_tag,boost::units::detail::static_rational_tag>
    {
      template<class T0, class T1>
      struct apply
      {
        typedef boost::units::scale_list_dim<
          boost::units::scale<
            (T0::base),
            typename mpl::divides<typename T0::exponent, T1>::type
          >
        > type;
      };
    };
  }
}

The main problem is that boost::mpl::divides does not work for a scale_list_dim and a static_rational. Power works because boost::mpl::times is implemented in boost/units/detail/unscale.hpp. (In fact, my fix is the copy of that code, replacing "times" with "divides".)

I'll try to add the fix to the library, but it's my first time on boost trac, so I don't know how long that'll take.

Tue, 24 Mar 2015 21:41:13 GMT

Thanks! It would be greatly appreciated if you could submit this fix to Boost trunk.

Tue, 24 Mar 2015 22:20:01 GMT

Replying to Wouter Boomsma <wb@…>:

Thanks! It would be greatly appreciated if you could submit this fix to Boost trunk.

I'll try, I hope I'll have time to look into submitting on the weekend.

anonymous — Fri, 19 Feb 2016 17:43:58 GMT

The bug persists

anonymous — Thu, 25 May 2017 11:18:42 GMT

The bug persists. Patch by "petamas" fixes compilation problem. Thanks a lot!

status, version changed; resolution set

Jürgen Hunold — Tue, 02 Jan 2018 16:32:25 GMT

status new → closed
version Boost 1.55.0 → Boost Development Trunk
resolution → fixed

Final pull request https://github.com/boostorg/units/pull/27 merged in https://github.com/boostorg/units/commit/3c5d74a1e1ac244b31370f1baf74170942af1f2e