std::chrono & Boost.Units

Question

I'm working on a software design in which I'd like to leverage Boost.Units. Some of the units I'd like to use represent time, however, I'm inclined to use the C++11 std::chrono units for those since they're standard.

I'm wondering if there's any clean integration between Boost.Units and chrono or whether I have to resort to writing my own converters and lose type safety by just copying scalar values between the types.

Are there any best practices for this issue?

Answer 1

If you just want to convert a std::chrono duration to a boost time quantity you can use the following template function:

using time_quantity = boost::units::quantity<si::time, double>;

template<class _Period1, class _Type>
time_quantity toBoostTime( chrono::duration<_Type, _Period1> in)
{
  return time_quantity::from_value(double(in.count()) * double(_Period1::num) / double(_Period1::den) );
}

One thing to note is that the returned time_quantity will always be in seconds and the storage type will be of type double. If any of those two are a problem, the template can be adapted.

Example:

namespace bu = boost::units;
namespace sc = std::chrono;
using time_quantity_ms = bu::quantity<decltype(bu::si::milli * bu::si::second), int32_t>;

std::cout << "Test 1: " << toBoostTime(sc::seconds(10)) << std::endl;
std::cout << "Test 2: " << toBoostTime(sc::milliseconds(10)) << std::endl;
std::cout << "Test 3: " << static_cast<time_quantity_ms>(toBoostTime(sc::milliseconds(10))) << std::endl;

/* OUTPUT */
Test 1: 10 s
Test 2: 0.01 s
Test 3: 10 ms