Re: [boost] Boost Units library preview

From: Deane Yang (deane_yang_at_[hidden])
Date: 2006-08-26 10:55:47

Andy Little wrote:

>> Can the dimension checking part of the library be used without the SI
>> unit system? For most other unit systems I use, I mainly need
>> dimension checking and not conversions between different units, such
>> as km or m? Thus just a quantity with dimensions would be useful to
>> catch programming errors.
> 
> Yes.  In the signature fixed_quantity<Unit, ValueType>, the Unit parameter can 
> be so modelled that it only allows base units to be used, and in this case there 
> is no conversion overhead BTW, a multiply is simply a multiply of the numeric 
> values for example).  By default Quan wont work across Unit models (IOW the 
> class template names of units must match), which means that attempting to do 
> calculations between Units with different class template names will fail at 
> compile time. By this means you can guarantee that you can prevent any 
> conversions. (FWIW there is also the option to allow  unit conversions but make 
> them explicit, prompted by Deane Yang easrlier in this thread.)
> 

I guess I wasn't particularly clear earlier in this thread, because 
fixed_quantity appears to be what I want. I'm sorry for not RTFM (I did 
try to read the documentation once, but my memory is not what it used to 
be), but I have two quick questions:

1) Does operator*(fixed_quantity<Unit1, ValueType1> x, 
fixed_quantity<Unit2, ValueType2> y) work and, if so, what is the result 
type, assuming that operator*(ValueType1 v, ValueType2 w) returns a 
ValueType3?

2) Can you raise a fixed_quantity to a rational power (I personally only 
need the power 1/2)?

Deane