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Subject: Re: GNAT.Sockets: Timeval_Duration is in milliseconds?
Date: Sun, 9 Dec 2007 07:55:02 -0800 (PST)
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Date: 2007-12-09T07:55:02-08:00
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On Dec 9, 4:33 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Sat, 08 Dec 2007 19:45:53 -0600, tmo...@acm.org wrote:
> >   The Ada 95 LRM 9.6(7) says
> > "...; a value of type Duration is used to represent the length of
> > an interval of time, expressed in seconds."
>
> > It would be bad practice to use a value of type Duration to represent,
> > say, the number of gallons of gasoline remaining, and it would be even
> > worse, because even more confusing, to use it to represent a number
> > of milliseconds.
>
> Sorry but this makes no sense. The physical entity being measured is
> duration T. Gallon is a measure of volume L**3. Clearly T /= L**3. As for
> seconds, milliseconds, years, centuries etc, all they fall under the
> category T (duration). They are numbers expressing the *same* physical
> entity. It is rather instructive to use the same type for them when
> possible.
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de

Conceptually you're right, but many annoying bugs are introduced by
assuming wrong scale when using same entities (feet/meter, T(K)/t(C),
X/Y/Z coordinates, etc.) In order to make the language work for you
one should go with different types.  My favorite is X,Y,Z coordinates:
all measure distance but misinterpreting those may case a trouble.  So
by introducing the new types for each plus one direction-less Distance
type will be good safety measure while all three are distance
entities.

Regards,
George Privalov.