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From: "Nick Roberts" <nickroberts@adaos.worldonline.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: List Container Straw Man
Date: Thu, 8 Nov 2001 19:09:37 -0000
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Date: 2001-11-08T19:09:37+00:00
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"Ehud Lamm" <mslamm@mscc.huji.ac.il> wrote in message
news:9sdnva$dpk$1@news.huji.ac.il...
> ...
> Am I right in _comparing_ (not equating) your approach to having an
ancestor
> type like Object or ANY, that all element types are derived from - thus
> ensuring a common interface?

Not really. My approach (as Ted's) uses generic packages instantiated with
the element type. I use a hierarchy of tagged types to represent iterators
(of gradually increasing complexity) based on that element type: it is this
which ensures a common (iterator) interface.

Typeless (nominally typeless), and 'reflective', languages, such as
Smalltalk, can get away with having containers based on a single root
element class, because the containers are always able to adapt sufficient to
cope with any element object thrown at them. Ada is not like this.

As regards my proposal, the element type must be definite. However, nothing
stops it being an access-to-classwide type:

   type Object_Ref is access all Object'Class;

allowing stores to deal, indirectly, with objects of all sorts whose types
are derived from Object.