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From: "Ludovic Brenta" <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Basic Explaination of OO in Ada
Date: 19 Sep 2006 09:06:33 -0700
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Date: 2006-09-19T09:06:33-07:00
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Alex R. Mosteo wrote:
> Just a note: although what Ludovic writes is right, and you can only have
> vanilla arrays of definite types, you can have more sophisticated
> containers (for example Ada.Containers.Indefinite_Vectors) that store
> class-wide types in Ada 2005:
>
> package Pak_Vectors is
>   new Ada.Containers.Indefinite_Vectors (Positive, Pak.T'Class);
>
> In this case, however, you store copies so some overhead can occur, but in
> many cases it can be more convenient than starting to play with pointers.

Doesn't Ada.Containers.Indefinite_Vectors have to declare a class-wide
access type for its internal use? I'd guess so. But, it hides the
access type from the user, and that's encapsulation at its best.

In Ada, one rarely needs access types at all. The only justification
for declaring one is because you're doing some kind of dynamic data
structure and allocating dynamically on the heap. With the standard
Ada.Containers, you'd need access types even less often.

That's why in my examples I did not declare an access type along with
the tagged type (in package P); instead, I declared an access type in
another package (package Collection) because that package absolutely
needed one.

-- 
Ludovic Brenta.