@mgriebling @jasonbobier Interesting, I've open sourced swift-measures last year.
- It has basic units, as well as many derived units that Foundation doesn't have. You can find the list in this DocC I made.
- There's also all the binary and metric ISO prefixes
The Measure object could easily have a generic type for its value.
Interestingly too I pitched the Rational type last year for Google Summer of Code. It was not accepted on the programme, however I still open sourced my work. It's incomplete and would need more thoughts.