For instance, physical dimensions store values as SI units, regardless of supplied unit, but retain the supplied unit type as a display hint.
Here, the Length dimension illustrates working with amounts of any unit.
Length orbit = 250 mi;
Length moon = 238000 km;
Length landing = moon + orbit;
display(landing); // prints 148,136.344 mi
display(landing.to(km)); // prints 238,402.336 km
// where
display(landing.to(mi) == landing.to(km)); // prints true
// perhaps a better example
Rate rate = 1.41 km/s;
Time duration = 76 hours;
Length distance = rate * duration;
// make your own unit constants
RateUnit kps = km/s;
rate = 1.41 kps;
You can play with the manifold-science[1] project, it implements the complete SI physical dimensions and many derived dimensions along with comprehensive operator overloading[2] support etc. to make working with and reading code using quantities more productive in Java.
1. https://github.com/manifold-systems/manifold/tree/master/man...
2. https://github.com/manifold-systems/manifold/tree/master/man...
Feels like it should be
Then methods like .plus() wouldn't even be defined for incompatible currencies. Of course that doesn't work for .equals(), so you'd still have to fall back to exceptions in that case.