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From: "Robert I. Eachus" <eachus@mitre.org>
Subject: Re: Ada and Java. different behaviour. casting long to int problem.
Date: 1999/06/17
Message-ID: <37694942.2C87628A@mitre.org>#1/1
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Date: 1999-06-17T00:00:00+00:00
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Marin David Condic wrote:
>                                 If one wants wraparound semantics, then
> perhaps there should be a special type to support that behavior - a la
> modular types in Ada. (Although these don't contain negative numbers and
> that may be a requirement.) In some cases, saturation semantics are a
> good thing, but again, this is not the "normal" understanding of
> arithmetic and therefore should be supported by a special type.
 
      Interesting question, but far from this topic...  If you want a
type with negative numbers that wraps around in Ada, how do you do it? 
Pragma Suppress is the easiest solution, but it is not guarenteed to
work portably, or even to work at all.  You can derive a type from a
modular type and override the comparison operators, etc.  This is
probably the best route.  The cleanest way from a users point of view is
probably to derive from Integer and override the arithmetic operations. 
This does have the problem with reemergence of the predefined operators
(see RM 12.5(8)) in a generic when one of these types is passed as a
generic formal integer type rather than a generic formal derived type.  
However, I think that this is probably the right behavior--let the
author of the generic worry about overflow inside the generic.  If you
want to use the redefined operators, you can always pass them as genric
formal subprograms.

      To bring this discussion back on topic, probably the best solution
for compilers that want to interface cleanly with Java, is to provide an
Interfaces.Java package, with an explicitly non-standard integer type
that can be converted to and from an Ada integer type.

-- 

                                        Robert I. Eachus

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