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From: sjw <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Question on types conversions - operations
Date: Sat, 13 Jun 2009 09:59:53 -0700 (PDT)
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Date: 2009-06-13T09:59:53-07:00
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On Jun 13, 4:51=A0pm, Olivier Scalbert <olivier.scalb...@algosyn.com>
wrote:

> I have the following three types:
> =A0 =A0 =A0type Length is new Float;
> =A0 =A0 =A0type Time =A0 is new Float;
> =A0 =A0 =A0type Speed =A0is new Float;
>
> Suppose I need to compute a speed given a length and a time.
>
> =A0 =A0 =A0L: Length :=3D 100.0;
> =A0 =A0 =A0T: Time =A0 :=3D =A010.0;
> =A0 =A0 =A0S: Speed;
>
> How to do that ?
>
> With S :=3D Speed(Float(L) / Float(T)) ? Mmmm ... not nice.
>
> With S :=3D Speed(L / Length(T)), I am also not satisfy as I convert a
> time in Length ...

You could declare functions such as "*" (s : speed; t : time) return
length and of course "*" (t : time; s : speed) return length.

Inside, you could use
  return length (float (s) * float (t));

You could use speed'base, time'base but then what if one is
long_float?

It's always seemed a lot of work for very little gain to me, I've
declared them as subtypes rather than types and left checking for the
right answer to unit test. But then, my world is all about logic and
there are far more enumerations than reals, and very few calculations.
Also, we tend to have coordinates (x, y) or (r, theta) so it's a lot
more useful to define "*", "+" etc.