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Date: Sun, 09 Dec 2007 13:50:08 +0100
From: Gautier <gautier@fakeaddress.nil>
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Subject: Re: GNAT.Sockets: Timeval_Duration is in milliseconds?
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Date: 2007-12-09T13:50:08+01:00
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Dmitry A. Kazakov wrote:
> On Sat, 08 Dec 2007 19:45:53 -0600, tmoran@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.

I think it Tom's point: it is so absurd that it is less likely to be mixed.

> As for seconds, milliseconds, years, centuries etc, all they fall under the
> category T (duration). They are numbers expressing the *same* physical
> entity.

Not exactly: the unit for Duration is a second, not a millisecond. I guess it's 
why it is not a floating type, but a fixed one. The SI unit for time is the 
second, not the millisecond; for weight it is the kilogram, not the gram. If 
parts of your program think that a second is worth 1000.0 with type Duration and 
others think that it is 1.0, you are in trouble - imagine a delay statement that 
controls the opening of a door in a space station! HAL, please!
______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

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