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From: lutz@iks-jena.de (Lutz Donnerhacke)
Newsgroups: comp.lang.ada
Subject: Re: Sugestion to Multiple Inheritance
Date: Mon, 21 Jan 2002 11:23:31 +0000 (UTC)
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* Matthew Heaney wrote:
>"Lutz Donnerhacke" <lutz@iks-jena.de> wrote in message
>> Exactly. Matthew showed also the impact of multiple inheritance by
>> duplicating the multiple included structure A. I'm pretty sure to find
>> a way without MI. Simply by designing the whole type more carefully and
>> use derivated packages.
>
>It's not clear what you're trying to do here, using a type hierarchy.
>
>Do you want a generic algorithm, that works for any kind of collection?

Yes.

>If so, then what's wrong with the model that the C++ STL uses?  It doesn't
>use tagged types, just generics.

Generics does not provide an abstract interface fullfilled by different
implemenations. I.e. a list-collection may generate a forward_iterator.
An algorithm requires forward_iterators aof any kind. The list-collection
might be instantiated by an array of limited types or a single-linked-list.
But every instatiation should provide the full interface of the iterator and
collection abstraction.

Sorry for beeing so vague, I'm still looking for a solution.

>You can do something very similar in Ada95:
>
>generic
>   type Iterator_Type is private;
>   with function Is_Less (L, R : Iterator_Type) return Boolean is <>;
>   with procedure Swap (L, R : Iterator_Type) is <>;
>   with function "+" (L : Iterator_Type; R : Integer)
>      return Iterator_Type is <>;
>   with function "-" (L : Iterator_Type; R : Integer)
>      return Iterator_Type is <>;
>   with function "-" (L, R : Iterator_Type)
>      return Integer is <>;
>   with function "<" (L, R : Iterator_Type)
>      return Boolean is <>;
>   with function "=" (L, R : Iterator_Type)
>      return Boolean is <>;
>procedure Generic_Quicksort
>  (First : in Iterator_Type;
>   Back  : in Iterator_Type);
>
>This will work for any collection that has an iterator.  It even works for
>arrays.  The algorithm itself doesn't know anything about the collection
>type or the item type.

Exactly. I thought about:
 generic
    type Iterator_Type is new Forward_Iterator with private;
 procedure Generic_XXX

getting the necessary interface from an abstaction.