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From: AdaMagica <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Question on types conversions - operations
Date: Mon, 15 Jun 2009 03:33:19 -0700 (PDT)
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Date: 2009-06-15T03:33:19-07:00
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On Jun 15, 10:40=A0am, Jean-Pierre Rosen <ro...@adalog.fr> wrote:
> sjw a =E9crit :>> With S :=3D Speed(Float(L) / Float(T)) ? Mmmm ... not n=
ice.
>
> Why not nice? You are performing (for good reasons) a non homogenous
> operation. Therefore you go to the no-dimension world (convert to
> Float), do your operation there, then return to the dimensioned world
> (convert to Speed).

Of course not nice because: You introduce different types for safety
against mixing different units incorrectly. But then you render
physical expressions unreadable by marring them with type conversions
- and you lose type checking. So where is the safety?

This is only OK when hidden in a body for overloaded versions of
multiplying operators.

But then:
With only three dimensions, there are only a few overloadings
necessary; *but* there are also only very simple expressions so that
it's improbable that you write wrong expressions. So what do you gain?
Do you really gain something? Wrong dimensions deliver abstruse
results which should show up immediately in unit tests (when done
properly).

For more dimensions, you get a nightmare of overloadings. So IMHO it
is complete nonesense to try to implement different dimensions with
different types like this (with compile-time checking).

IMHO, there is no good way to do this in Ada as she is now.