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From: "Nick Roberts" <nickroberts@adaos.worldonline.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: List Container Straw Man
Date: Sun, 11 Nov 2001 03:48:00 -0000
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Date: 2001-11-11T03:48:00+00:00
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"Ehud Lamm" <mslamm@mscc.huji.ac.il> wrote in message
news:9sk0mc$39j$1@news.huji.ac.il...
> ...
> My problem is on a more semantic level. To understand your approach
students
> must understand about inheritance (or so it seems to me). It is not like
> instanating Integer_IO, which results in having "normal" procedures.
> ...

Not really. Having cited the magic incantation:

   package Widget_Iteration is new SCL.Iteration(Widget_Type);
   package Widget_Lists is new SCL.Lists.Unbounded(Widget_Iteration);
   subtype Widget_List is Widget_Lists.Unbounded_List;

your students can (at first) use the type Widget_List straightforwardly
without having to touch upon anything to do with inheritance, e.g.:

   L: Widget_List;
   W: Widget_Type;
   ...
   while not End_of_File(F) loop
      Read_Widget(F,W);
      Append(L,W); -- add to end of list L
   end loop;

and so on. Later on in the course (much later), when they have done tagged
types, inheritance, abstract types, generic packages, signature packages,
etc., you can then introduce them to the idea of defining a procedure that
can work with different container types, e.g.:

   function Count (
      Widget: in Widget_Type;
      Within: in out Widget_Iteration.Sequence_Producer'Class) return
Natural;

and so on.

--
Best wishes,
Nick Roberts