But cant you just implement operator+(celcius, celcius) that will do the conversion to kelvin and back, since you know for certain the conversion math?
Adding temperatures is not done usually. Mixing substances adds thermal energy. There's no reason I can hink of why allowing plus operator on temperatures is a good idea. You can add temperature differentials, but it is plain addition so long as units are in agreement. And 0C differential is 0F differential, no offsets in conversions.
I did that, but then adding 0_degC + 0_degC gave 273.15_degC. I think that would be surprising to many people. In reality I don't remember ever having to deal with physics formulas that used °C instead of Kelvins, so the only time I need to use °C is when presenting the temperature in the UI:
