Re: [Boost-users] [Units] Un-scaling dimensionless value

AMDG On 02/17/2014 07:40 AM, Lindley French wrote:

For the life of me I can't figure out where the actual multiplication of the value occurs. Boost Units is very clever template magic, but I doubt anyone could maintain the thing without weeks of studying the design....

detail/conversion_impl.hpp:345 return(destination_type::from_value(static_cast<T2>(source.value() * conversion_factor(u1, u2)))); This won't really help you because the result of conversion_factor returns a double. The scale is evaluated at detail/conversion_impl.hpp:448 return(conversion1::value() * (scale::value() / conversion2::value())); "scale" here is the result of get_scale_list/eval_scale_list. get_scale_list collects the scaling factors, eval_scale_list multiplies their ::value() together. Again, scale::value() returns a double, because the individual scale factors use double. (See scale.hpp)

On Mon, Feb 17, 2014 at 9:48 AM, Lindley French wrote:

...

What's the best way to access the current scaling of a dimensionless value? Maybe I can back it out myself rather than relying on type conversion to do it.

There's a metafunction called get_scale_list, which returns an MPL sequence whose members contain static const long base = ...; typedef static_rational<...> exponent; It's not documented, so use it at your own risk. It's unlikely to change, but I make no guarantees. In Christ, Steven Watanabe