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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Generic Collection
Date: Sat, 12 May 2007 08:18:09 +0100
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Date: 2007-05-12T08:18:09+01:00
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andrew <andrew.carroll@okstate.edu> writes:

> So I think you are saying I would have one Collection package and it
> has three procedures called Add and they operate on three different
> types:
> Tuple
> Table
> Schema
>
> but then how do I later use the collection package for some other
> purpose?

I would probably end up with a package for each, with appropriate Add
operations.

with Tuples;
package Tables is
  type Table is private;
  procedure Add (To : in out Table; Item : Tuples.Tuple);
  ...
private
  ...
  package Tuple_Containers
  is new <generic-container-package> (Items => Tuples.Tuple);
  type Table is record
    Items : Tuple_Containers.Container;
    ...
  end record;
  ...

where you get the fun of choosing which generic-container-package to
use (Ada.Containers would be a good start) or writing your own.

I can't see what possible advantage you'd get from being able to add a
Colour to a Schema! If you make a container that can contain anything
you will need to have runtime checks to enforce this sort of rule
rather than compile-time checks. Elsewhere in this thread you seemed
to scoff at this as being a concern; I think classwide programming
ought to be restricted to the places where it brings you an advantage
rather than being something that makes your life difficult.