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

AMDG On 12/15/2010 10:12 AM, alfC wrote:

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

The ability to test for a conversion is liable to result in ODR problems. On the other hand, the errors are pretty horrendous right now. This is a fairly common problem. Could you file a trac ticket. I'll try to make the error more readable. In Christ, Steven Watanabe