From: Patrick Hohmeyer <pi3_1415926536@yahoo.ca>
Subject: Re: Another Idea for Ada 20XX
Date: Sun, 2 Dec 2001 16:19:08 -0500
Date: 2001-12-02T16:19:08-05:00 [thread overview]
Message-ID: <ezwO7.1091$iF3.275822@news20.bellglobal.com> (raw)
In-Reply-To: 3C0A5054.E74A82E7@worldnet.att.net
James Rogers wrote :
> In scientific terms a measurement is done in terms of some unit.
> For instance, distance is in meters, microns, feet or furlongs.
> Speed is then calculated as a distance per unit time. Acceleration
> is the second derivative of speed.
Acceleration is the second derivative of *distance*. ;-)
> The advantage for the software developer is in the usage:
>
> Vehicle_Speed : Speed;
> Track_Distance : Meters;
> Lap_Time : Hours;
>
> Speed := Track_Distance / Lap_Time;
>
> This approach would allow the appropriate mixing of data types, which
> is currently forbidden by Ada, in a meaningful and correct manner.
>
Hmm, this can very easly be achived with overloading of "/" :
function "/" (Dist : Meters; Time : Hours) return Speed is
--...
And I have a huge problem with the name of the type Speed.
Speed is not a unit, but an concept.
Would be more interesting :
type Distance is basic concept with basic unit Meters;
type Time is basic concept with basic unit Seconds;
type Speed is concept (Distance / Time);
Vehicle_Speed : Speed; -- ok
Track_Distance1 : Meters; -- ok
Track_Distance2 : Meters := 12.5; -- ok
Lap_Time1 : Time; -- ok
Lap_Time2 : Time := Seconds(34.3); -- ok
Lap_Time3 : Time := 34.3;
-- 2 possibles reactions :
-- 1. won't compile as the unit isn't specified !!! (my favor)
-- 2. uses the basic unit for the concept (Seconds)
-- (but generates a compiler warning)
Vehicle_Speed := Track_Distance1 / Lap_Time1; --ok
Internally a concept type would be something as
record
Value : Double;
Unit : Unit_type;
end record;
Unit somehow describes how we can transform the value
into a value in the basic units. (an access to a function?)
and vice-versa.
The great part are unit extentions :
type Hours is Time unit 3600 Seconds;
S : Seconds := 3954.3;
H : Hours := S;
And the compiler would automagicly put 3954.3 / 3600 into H.
As would the cast Hours(S) return 3954.3 / 3600;
Especially for Space programs between US and Europe this would
be a *huge* benefit.
Just declare :
type Inchs is Distance unit x Meters;
and the compiler will do all unit conversions for you.
And of course :
type Temperature is basic concept with basic unit Kelvin;
type Celsius is Temperature unit 1 Kelvin + 273.15;
And a non-basic concept :
type Mass is basic concept with basic unit Kilogram;
type Acceleration is concept Speed / Time;
type Force is concept Mass * Acceleration;
type Newton is Force unit 1 (Kilogram * Meters * Seconds**(-2));
(Note that :
type Newton is Force unit 1
(Kilogram * Meters * Seconds**(-1) * Hours**(-1));
would also be syntaxly correct, you can mix 2 time units in a
composed unit.)
I think that this could be fun, but may be to complicated to
implement and if you really need it, can already be done with
a record and an access to fonction for the unit type,
and a lot of overloaded functions.
But what do you think ?
--
Patrick Hohmeyer
next prev parent reply other threads:[~2001-12-02 21:19 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-12-02 16:01 Another Idea for Ada 20XX James Rogers
2001-12-02 16:38 ` Preben Randhol
2001-12-02 22:26 ` James Rogers
2001-12-02 21:19 ` Patrick Hohmeyer [this message]
2001-12-02 21:26 ` Lutz Donnerhacke
2001-12-02 23:49 ` Patrick Hohmeyer
2001-12-03 6:06 ` Wilhelm Spickermann
2001-12-03 8:58 ` Lutz Donnerhacke
2001-12-03 13:40 ` Thomas Koenig
2001-12-03 0:21 ` Robert C. Leif, Ph.D.
2001-12-03 0:35 ` Robert Dewar
2001-12-03 1:33 ` James Rogers
2001-12-03 12:34 ` Dirk Dickmanns
2001-12-04 19:02 ` Unit handling (was: Another Idea for Ada 20XX) Wilhelm Spickermann
2001-12-03 14:56 ` Another Idea for Ada 20XX Mark Lundquist
2001-12-03 15:12 ` Lutz Donnerhacke
2001-12-03 21:13 ` Dimensionality Checking (Ada 20XX) Nick Roberts
2001-12-04 14:00 ` Dmitry A. Kazakov
2001-12-06 19:52 ` Britt Snodgrass
2001-12-06 20:55 ` Mark Lundquist
2001-12-06 22:38 ` Wes Groleau
2001-12-06 23:12 ` Mark Lundquist
2001-12-07 14:36 ` Wes Groleau
2001-12-07 9:37 ` Dmitry A. Kazakov
2001-12-07 22:51 ` Mark Lundquist
2001-12-03 17:00 ` Another Idea for Ada 20XX chris.danx
-- strict thread matches above, loose matches on Subject: below --
2001-12-02 19:51 Gautier Write-only-address
2001-12-02 22:36 ` James Rogers
2001-12-03 12:44 ` Marc A. Criley
2001-12-03 14:29 ` Larry Kilgallen
2001-12-04 0:25 ` Marc A. Criley
2001-12-04 1:40 ` Adrian Hoe
2001-12-04 1:56 ` Larry Kilgallen
2001-12-04 16:08 ` Wes Groleau
2001-12-04 17:48 ` Larry Kilgallen
2001-12-09 23:02 ` Nick Roberts
2001-12-10 16:22 ` Stephen Leake
2001-12-10 17:11 ` Wes Groleau
2001-12-10 20:30 ` Robert C. Leif, Ph.D.
2001-12-10 20:59 ` Wes Groleau
2001-12-10 17:09 ` Wes Groleau
2001-12-10 17:32 ` Larry Kilgallen
2001-12-04 19:59 ` Vincent Marciante
2001-12-04 20:20 ` Wes Groleau
2001-12-04 22:18 ` Matthew Heaney
2001-12-06 4:14 ` Richard Riehle
2001-12-06 17:39 ` Wes Groleau
2001-12-07 0:55 ` Adrian Hoe
2001-12-07 9:01 ` Dmitry A. Kazakov
2001-12-07 11:49 ` Tarjei T. Jensen
2001-12-03 14:56 ` Mark Lundquist
2001-12-06 15:27 ` Philip Anderson
2001-12-07 22:51 ` Mark Lundquist
2001-12-10 9:01 ` Dmitry A. Kazakov
2001-12-02 21:24 Gautier Write-only-address
2001-12-03 14:56 ` Mark Lundquist
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