Re: [boost] Boost Units library preview

From: Matthias Troyer (troyer_at_[hidden])
Date: 2006-08-23 05:23:19

On Aug 22, 2006, at 1:43 AM, Eric Lemings wrote:

>
>
>> -----Original Message-----
>> From: boost-bounces_at_[hidden]
>> [mailto:boost-bounces_at_[hidden]] On Behalf Of Matthias Troyer
>> Sent: Saturday, August 19, 2006 1:55 AM
>> To: boost_at_[hidden]
>> Subject: Re: [boost] Boost Units library preview
>>
>>
> ...
>> If I understand the above concepts correctly then we only need three
>> terms:
>>
>> - named unit
>> - unnamed unit
>> - quantity (value + unit)
>
> I try to keep the definitions as simple as possible.  IMHO, there are
> really only four distinct concepts:
>
> dimension - an "abstract" type
> quantity - an "abstract" object whose "type" is a dimension
> unit - a type "derived" from a particular dimension
> measure - an arithmetic object whose "type" is a unit
>
> The last term is a term I introduced to distinguish an object with a
> dimension from an object with a unit.  Very important distinction.
>
> Eric.

Let me check if I understand this correctly in one example.

- Nm would be a "dimension"
- 1 Nm would be a "quantity"
- a torque measured in Nm or an energy measured in Nm would be two  
distinct units
- 1 Nm as torque, 1 Nm as energy or 1 J as energy would be three  
distinct measures

If that is correct then I have several comments, but please check my  
understanding first.

Matthias