[Boost-users] [units] check if quantities are convertible one into the other

Subject: [Boost-users] [units] check if quantities are convertible one into the other
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-12-15 13:12:40

Hi, 

 I have two (or more) default (or user defined) system units. For certain 
operations I assume that one quantity in one system can be converted into 
another quantity in some other system with the same dimension. What 
conversions are allowed depend on the included headers at best. 

What is the best way to check at compile time that one quantity can be 
converted into another?

For example, I have this function that sums two quantities with the same 
dimension and returns the result of the left term. The function assumes that 
qright is convertible to qleft. If it is not convertible I would like to 
catch the error early with static_assert (or even with some enable_if to 
ignore the function)

    template<class Dimension, class LeftSystem, class RightSystem>
    quantity< unit<Dimension, LeftSystem> > sum_to_left(
        quantity< unit<Dimension, LeftSystem> > const& qleft, 
        quantity< unit<Dimension, RightSystem> > const& qright
    ){
        return boost::units::operator + (qleft, quantity< unit<Dimension, 
LeftSystem> >(qright));
    }

Thank you,
Alfredo