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From: falis@ma.aonix.com (Ed Falis)
Subject: Re: How to write TYPECASE in Ada 95?
Date: 1999/02/06
Message-ID: <1103_918264881@DZOG-CHEN>#1/1
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References: <79fct8$9k3$1@murdoch.acc.Virginia.EDU>
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Organization: Aonix, San Diego, CA, USA
Newsgroups: comp.lang.ada
Date: 1999-02-06T00:00:00+00:00
List-Id: <comp.lang.ada>


> On 5 Feb 1999, Norman Ramsey wrote:
> > 
> > I'm trying to figure out from the reference manual how to identify
> > which type extension of a type I have.  For example, if I have
> > 
>
> > I'd like to be able to discriminate at run time:
> > 
> >    p : Point;
> > 
> >      ...
> > 
> >    if p in Painted_Point then
> >       ... do something with Painted_Point'(p)
> >    else if p in Tall_Point then
> >       ... do something with Tall_Point'(p)
> > 
> > Even better would be something like Modula-3 TYPECASE:
> > 
> >   (* modula-3 *)
> >   TYPECASE p OF
> >   Painted_Point (painted) => ... do something with painted
> >   Tall_Point    (tail)    => ... do something with tall
> >     ...
> >   END
> > 
> > What's the idiomatic way to express this in Ada?

I thought a good part of the point of tagged types (and support for polymorphism in other OOP's) was exactly to avoid this kind of code.

- Ed