The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
// implementation of adding two ratios:
template<typename R1, typename R2>
struct RatioAddImpl
{
private:
static constexpr unsigned den = R1::den * R2::den;
static constexpr unsigned num = R1::num * R2::den + R2::num * R1::den;
public:
typedef Ratio<num, den> Type;
};
// using declaration for convenient usage:
template<typename R1, typename R2>
using RatioAdd = typename RatioAddImpl<R1, R2>::Type;