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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Ada vs Delphi?
Date: 1999/08/11
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Date: 1999-08-11T00:00:00+00:00
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In article <37b129ae.43419124@news.total.net>,
  aratel@total.net (Andre Ratel) wrote:
> -= Mixing types =-------------------------
>
> I'm not sure I fully understand. Let's say n1 and n2 are known
> to be non-negative integers (called cardinals in Delphi) but
their
> difference  might be positive or negative. In Delphi, I would
then
> declare these variables as
>
>   type
>     n1, n2: cardinal;
>     N21, N12: integer;
>
> and I could have something like
>
>   begin
>     n1:= 0;
>     n2:= 8;
>     N21:= n2 - n1;
>     Writeln(IntToStr(N21));
>     N12:= n1 - n2;
>     Writeln(IntToStr(N12));
>   end;
>
> This seems OK with me and, with range checking off, would give
the
> right answers (8 and -8). On the other hand, a statement like
>     Writeln(IntToStr(n1 - n2));
> would give  4294967288.
>
> Now, with the above definitions of variables, a statement like
>     N21:= n2 - n1;
> would not be valid with Ada?


You definitely do NOT understand, which is not surprising since,
as I expected, Delphi is not strongly typed in this area.

Your view of types above is strictly structural, you declare
things to be signed or unsigned according to their value range
and then worry about mixing these values.

That has nothing at all to do with the kind of strong typing
we are talking about, where you have:

  type minutes is range 0 .. 59;
  type seconds is range 0 .. 59;

  mm : m;
  ss : s;

Now mm and ss have IDENTICAL representation, but are of quite
different types, so an assignment

  mm := ss;

which is almost *certainly* a bug, is statically illegal, just
as illegal in fact as trying to assign a record to an integer.


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