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From: gpriv@axonx.com
Newsgroups: comp.lang.ada
Subject: Re: Are there noticable differences in Ada acceptance by country?
Date: Thu, 20 Mar 2008 15:59:25 -0700 (PDT)
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Date: 2008-03-20T15:59:25-07:00
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On Mar 20, 6:17 pm, Simon Wright <simon.j.wri...@mac.com> wrote:
> "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de> writes:
>
>
>
> > On Thu, 20 Mar 2008 20:22:22 +0000, Simon Wright wrote:
>
> >> gp...@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?

>From my own C experience: using code from different sources X and Y
coordinates in function calls were in different order: foo(x,y);
boo(height, width), etc. Easy to overlook.

George.

> 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?