On Aug 18, 2006, at 7:43 PM, Andy Little wrote:
"Eric Lemings" <lemings@roguewave.com> wrote in message
I think Thorsten's question is a sympotom of a larger issue.
Why does Quan use such convoluted terminology? Fixed quantity?
fixed_quantity is the name of the class template implemented so far ( one of 3 or possibly 4 different classes). It has gone through various names. Once just quantity, then ct_quantity, then t1_quantity, now fixed_quantity. It is a quantity where the Unit is fixed at runtime. All suggestions for alternate names are welcome.
Abstract quantity?
An abstract quantity is a quantity without a numeric value or a conversion factor. It still conforms to dimensional analysis and dimensional math. In fact the abstract quantity concept (small c) has now been gobbled up by the all encompassing Static Unit concept.
I am confused. What is a quantity without a numeric value? Just a unit? I don't see the reason for a quantity without a value. Just the name quantity implies a value.
Named quantity?
A named quantity has a name. In practise in Quan-0_2_0 this means that, where U is a model of StaticUnit and is_named_quantity<U>::value is true, that get_named_quantity_traits<U>::type , returns a traits class, which provides useful information, such as the name of the quantity and other information mainly useful for I/O purposes.
I assume that this mean that the unit has a special name, and additional information?
Concrete quantity?
A concrete quantity is a quantity which has a unit and a numeric value.
Same confusion as with abstract quantity. Isn't abstract quantity just the unit? I
Anonymous quantity?
An anonymous quantity doesnt have a name, kind of the opposite of a named quantity. is_named_quantity<U>::value is false for anonymous quantities in the next version of Quan, and so their Named Quantity Traits class is effectively void.
Does this mean that the name will be derived, like in m/s^2 ? Or that there is no unit symbol at all that can be printed? Again this seems to be a property of the unit of the quantity. Wouldn't unnamed unit be a better name?
Static unit?
This is a proper C++ Concept. Effectively its a compile time database which can be queried about various aspects of a particular fixed_quantity. It is a template parameter to fixed_quantity:
fixed_quantity<StaticUnit,NumericType>
United value?
It is a detail of the implementation. Has it leaked into the docs somewhere? If so I will remove it as it may change without notice.
A general-purpose library should use simple terms and a bare minimum of names.
If I understand the above concepts correctly then we only need three terms: - named unit - unnamed unit - quantity (value + unit) Matthias