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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Question on types conversions - operations
Newsgroups: comp.lang.ada
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Date: Sat, 13 Jun 2009 18:58:40 +0200
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Date: 2009-06-13T18:58:41+02:00
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On Sat, 13 Jun 2009 17:51:17 +0200, Olivier Scalbert wrote:

> I have the following three types:
>      type Length is new Float;
>      type Time   is new Float;
>      type Speed  is new Float;
> 
> Suppose I need to compute a speed given a length and a time.
> 
>      L: Length := 100.0;
>      T: Time   :=  10.0;
>      S: Speed;
> 
> How to do that ?
> 
> With S := Speed(Float(L) / Float(T)) ? Mmmm ... not nice.
> 
> With S := Speed(L / Length(T)), I am also not satisfy as I convert a 
> time in Length ...

Once you have said 'A', you have to say 'B':

function "/" (Left, Right : Length) return Length is abstract;
function "/" (Left, Right : Time) return Length is abstract;
function "/" (Left, Right : Speed) return Length is abstract;
function "/" (Left : Length; Right : Time) return Speed;

The first three disallow illegal operations on Length, Time and Speed.

The body of "/" is

function "/" (Left : Length; Right : Time) return Speed is
begin
   return Speed (Float (Left) / Float (Right));
end "/";

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de