Matthias Schabel wrote:
I'm not one of the people who initially requested this, but I can absolutely see a use for dimensional analysis when it comes to finances. Think of $/flop, watt/flop or even $-watt/flop for procuring computing systems.
Good point. Anyway, the library was designed to make implementing new unit systems relatively easy (as library implementation goes), so this kind of usage should be simple. For things like $/watt, you can even just extend the existing SI system...
(butting in) I'm not sure about that. You had two ideas, the first was to forward everything to the value_type, so you'll have a us_dollar value_type, etc. I thing it's not convenient. Most users will find something like quantity<currency/*, default to double*/> q1(1500.0 * us_dollar); makes more sense than quantity<currency, us_dollar> q1(1500.0); It certainly fits the rest of the library better, IMO. More than that, the second idea of extending the SI system pretty much, AFAIU, forces the value_type to *not* be anything like us_dollar - it should fit length and mass to! So I believe it boils down to providing a runtime-changeable conversion ratios for some units (currency), in addition to the currently fixed ratios for other units (physics). Whether or not you want to support it, is a completely different matter... Yuval