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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Are there noticable differences in Ada acceptance by country?
Date: Thu, 20 Mar 2008 22:17:18 +0000
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Date: 2008-03-20T22:17:18+00:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Thu, 20 Mar 2008 20:22:22 +0000, Simon Wright wrote:
>
>> gpriv@axonx.com writes:
>> 
>>> I think strong typing should not be dismissed.  Unfortunately Java-
>>> based (and C/C++/C#) courses don't explain to students that X and Y
>>> coordinates being fundamentally integer (or float) types are not the
>>> same thing.
>> 
>> I always disliked an X binding which had (sub)types for X, Y
>> coordinates. Wrong level of abstraction, I thought: use something like
>> 
>>    type Position is record
>>       X : Float;
>>       Y : Float;
>>    end record;
>> 
>> and you get a _lot_ less scope for confusion.
>
> If no rotations involved I would suggest:
>
>    type Horizontal_Coordinate is new Float;
>    type Vertical_Coordinate is new Float;
>    type Position is record
>        X : Horizontal_Coordinate;
>        Y : Vertical_Coordinate;
>    end record;
>
> In some cases I would consider making absolute positions and relative
> offsets different types, similar to Time and Duration.

Well, to be fair, I suppose I would have used Metres (or Pixels)
rather than plain Float.

  subtype Metres is Float;

But I don't see the real advantage in using different types for H_C
and V_C. How ofen are users actually going to get this wrong? There is
some comment-like advantage to subtyping -- rather like AdaCore's
library packages with eg

  subtype Path_Name is String;

but full typing is only going to clutter the place up with
conversions. Or perhaps you lie to provide all the operations a person
could need (acceleration x duration -> speed etc)?


Why would things be different if there were rotations involved?