On Thu, Jul 2, 2009 at 3:41 PM, Steven Watanabe<watanabesj@gmail.com> wrote:
Zachary Turner wrote:
On Thu, Jul 2, 2009 at 2:07 PM, Steven Watanabe<watanabesj@gmail.com> Thanks. The confusion came from the fact that the syntax I was trying was being used in some of the examples. But there is something different about those examples, so that's why it wasn't working. One of the trig examples has a line:
quantity<plane_angle> theta = 0.375*radians;
for example. I suppose it's due to the fact that radians are the "primary" unit for this dimension?
The difference is that plane_angle is the same unit as radians. In your case, data_capacity is defined as bits, while you are assigning it a value in bytes. Since the units change, the conversion is explicit.
Well what then do you think is the "correct" or "best" way to support what I'm trying to do? It seems like a fairly simple use case but at least to me anyway it's turning out to be rather confusing and complicated. For example, quantity<> is defined as template<class Unit> class quantity; yet one of the valid values for Unit is boost::units::dimensionless. So are we specifying a unit or a dimension? Clearly something that is dimensionless is also unitless but it seems inconsistent for values to be either units, or the empty dimension. The examples have many occurences of things such as quantity<si::length>, quantity<si::mass>, quantity<temperature>, all of which in a physical sense are dimensions. feet,yards,meters; kilograms, grams, ounces; fahrenheit, celsius, kelvin are all units. So I would expect to see quantity<fahrenheit>, quantity<ounces>, quantity<inches>, just based on the fact that the template argument is named Unit. However, all of the examples seem to define only 1 valid template argument for quantity per dimension per system. So if you want si mass then there's 1 thing you can pass to quantity<>, even though with all the prefixes there are a multitude of different units for mass that are still based on the si system. I agree that the template argument to quantity should be a unit, but then I would expect to be able to declare a quantity<> parameterized with every possible unit of length measurement, quantity<feet>, quantity<inches>, quantity<mm>, etc. with automatic conversions provided between every combination. Maybe I'm just doing it all wrong, I'm not trying to be a PITA or anything, at this point I really just want it to work :( Maybe units of data storage capacity could be incorporated into boost 1.40 since they're pretty common (especially for programmers), although ultimately it would still be nice if I could understand how to use the library. Thanks for your patience :) Zach