Phil Richards wrote:
On 2006-06-08, David Greene <greened@obbligato.org> wrote:
Andy Little wrote:
Complain to the SI people. It aint my fault guvnor!
But it's your library! Honestly, I think you are too constrained by some paper SI standard. There is nothing at all that says the library must be implemented this way.
The SI standard has been agreed to be implemented worldwide (and should already be according to the original intention). Including the USA and the UK (both dragging their feet). It isn't just *some* standard - it is *the* standard. Of course, the Boost units standard might someday supplant it, but, really, I doubt it.
But that doesn't have anything to do with the _implementation_ of the library. Andy presented this example to justify kg's 0 power: mass::kg m(1); // 1 kg == 1000 g acceleration::m_div_s2 a(1); // 1 meter per second squared force::N f = m * a; The value of f should be 1000 Newtons right? Of course, the value is 1 Newton. But this has nothing at all to do with kg having a prefix power of 0 or 3. The calculation can be done when assigning m*a to f. The compiler (though TMP techniques) knows that m*a is in kg*m/s^2. It knows it's being assigned to a value of N. It can look up the prefix powers (3 for kg in my suggestion) and "do the right thing." If that requires some special cases for conversions like this, it's better than forcing everyone who extends the system to keep track of which quantities follow the rules and which don't. And besides, as others have argued, a Boost units library needs to go beyond S.I. S.I. is far too narrow for many domains. -Dave