Re: Another Idea for Ada 20XX

[dmitry@elros.cbb-automation.de (Dmitry A. Kazakov)]

On 6 Dec 2001 16:55:38 -0800, byhoe@users.sourceforge.net (Adrian Hoe)
wrote:

>Wes Groleau <wgroleau@usa.com> wrote in message news:<3C0FAD3D.64ACC870@usa.com>...
>> 
>>   function "+" (Left   : Meters;
>>                 Right  : Kilometers)
>>                 return : Meters;
>
>Consider this:
>
>function "+" (Left   : Meters;
>              Right  : Inches)
>              return Meters;
>
>What kind of precision in the conversion of Inches to Meters if Unit
>Checking and Conversion are to be part of Ada? Do I/we have the
>liberty to select the precision I/we want?

A possible solution is that there should be same precision of Left,
Right and result. They should have exactly same representation [in
some unit system, like SI] and Inches would be just a view of some
length [which corresponds to the physical nature of meters and
inches]. So

    X : Inches := 5;  -- Means  X := 0.127 [m]

Unfortunately the price of this is that it will be impossible to have
precise computations in non-metric units and range problems [eV is
pretty small when compared with J].

However, it is thinkable [and preferable] that Ada would provide not
an implementation of some unit system, but rather facilities to do it.
Then of course, a user might just create its own unit system like
(foot, second, pound) and have meters as a view of feets. He would
also be able to create two different systems and define conversions
between them with necessary care of precision.

>How exactly this will be implemented by the new annex of Ada
>(perhaps)?

Regards,
Dmitry Kazakov