Re: [boost] Boost Units library preview

From: Matthias Troyer (troyer_at_[hidden])
Date: 2006-08-21 07:24:48

On Aug 20, 2006, at 8:36 PM, Andy Little wrote:

>
> "Matthias Troyer" <troyer_at_[hidden]> wrote
>
>> OK, this sounds reasonable enough, except that I'm still confused
>> what exactly an anonymous quantity is.
>
> I realise I didnt answer this question.
>
> In the calculation:
>
> force * distance;
>
> The programmer might be dealing with a force acting at a moment, or  
> the energy
> required to move an object.
> There is no way to tell from the calculation which. (One could  
> apply some
> angular tag to torque, but after experimenting with this I found it  
> rather vague
> and fussy).
>
> Therefore, as there is no way to tell which quantity is intended I  
> don't try, so
> the result is an anonymous quantity.
>
> One could apply various rules (for instance length * length -->  
> area), but as I
> can't apply a rule easily to the above case, I opted to apply the  
> same rule to
> every case of  dimensionful multiplication and division, which was  
> to return an
> anonymous quantity and leave it to the programmer to decide which  
> quantity they
> were dealing with.

As far as I understand, the named quantities just use special symbols  
then? Actually Nm is a valid unit for both energy and torque, but you  
sometimes want it printed as J and sometimes as Nm, and you use named  
quantities to force this? Is this correct?

Matthias