Re: [boost] Boost Units library preview

From: Matthias Troyer (troyer_at_[hidden])
Date: 2006-08-24 09:05:31

On Aug 24, 2006, at 7:24 PM, Andy Little wrote:

>>
>> energy = force*distance; // should this be allowed?
>> torque = force*distance; // should this be allowed?
>
> Quan allows this as it stands.

Good.

>
>> I think that in both cases the implicit conversion from the
>> (annonymous?) quantity force*distance to either energy or torque. I
>> think that to make the library usable one needs to allow these
>> conversions.
>
> The temporary result of force * distance is a so-called anonymous  
> quantity.

OK

>
>> If one want to prevent the operations then because one is a vector
>> scalar product (the energy) and the other a vector cross product (the
>> torque) then this should be done at the level of the value_type of
>> the quantity and not at the unit level.
>
> Yes the obvious way to make a quantity a vector quantity is simple.  
> Put it as
> the value_type of a vector. Currently quan has 2D and 3D vectors in  
> separate
> namespaces, but it was suggested that it would be more flexible to  
> just have a
> quan::simple_vector<N_dimensions,quantity> and hopefully that will be
> implemented at some stage.

Why not just use a ublas vector or MTL vector with a quan quantity?  
As i mentioned before I see no reason for reinventing the wheel. I  
still have not seen your reason for having your own vector classes.

Matthias