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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: How to write TYPECASE in Ada 95?
Date: 1999/02/18
Message-ID: <m3emno55ab.fsf@mheaney.ni.net>#1/1
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NNTP-Posting-Date: Thu, 18 Feb 1999 03:15:31 PDT
Newsgroups: comp.lang.ada
Date: 1999-02-18T00:00:00+00:00
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tmoran@bix.com (Tom Moran) writes:

> >If you want to extend a type with arbitrary behavior, you could take a
> >look at using the Visitor pattern.  Ada implementations of this pattern
> >are available at the ACM patterns archive.
> 
> ><http://www.acm.org/archives/patterns.html>
> Am I looking at the right place?  I see
> 
> >package body Equipment.Pricing is
> 
> 
> >   function Get_Total_Price
> >     (Equipment : Root_Equipment'Class) return Dollars is
> >   begin
> >      if Equipment in Floppy_Disk then
...
> which surely looks pretty similar to
> 
> > procedure Serve_Fruit(Dish : in Fruit'class) is
> >  begin
> >    if Dish in Apple'class then Serve(Apple(Dish));
> >    ...
> >    elsif Dish in Watermelon'class then Serve(Watermelon(Dish));



Indeed, you are correct.  The was the last of 3 versions of the visitor
pattern I sent to the list, and I discuss the pros and cons of each
approach in the accompanying text.