Michael Walter wrote:
How would you store the products? I don't really like the idea of unintuitive limits on the composition of base units (e.g. you can represent 2^31, but not 19^31)
I might have been a bit imprecise here, so please consider: const unsigned int Time = 2; const unsigned int Length = 3; const unsigned int Mass = 5; const unsigned int Current = 7; const unsigned int Temp = 11; const unsigned int Amount = 13; const unsigned int Intensity = 17; template <unsigned int N, unsigned int D=1> struct Rational { ... }; typedef Rational<Time> time; typedef Rational<Length> length; typedef Rational<Mass*Length,Times*Times> force; typedef Rational<Mass*Length*Length,Times*Times> energy; quantity<energy, double> e; so the representation of energy would be just 5*3*3/2*2 = 45/4. You're right, there is a computational limit, but I wouldn't expect to a see a dimension with the power of 31. Exponends of 4 are about the highest I've ever seen, and (2*3*5*7*11*13*17)^3 still fits in 57 bits, so we might want to use long or even long long unsigned ints, but that should be fine for most situations. Andreas