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From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: Question about OO programming in Ada
Date: Tue, 25 Nov 2003 21:55:25 +0100
Organization: AdaCL
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Ekkehard Morgenstern wrote:

> 
> Hi guys,
> 
> I have a question about object-oriented programming in Ada:
> 
> Do I have to use class-wide types for object-oriented programming, or
> could I use regular access types?
> 
> Like, when I declare a procedure
> 
>     procedure A ( B: in access all T'Class )

I made this mistake as well when I started. For OO it should be only:

procedure A ( B: in out T )

Unlike C++ no access is needed in Ada. And a class wide Types make your
procedure non "virtual". Some Tutorials are quite bad about describing that
point.

> could I use a different method and still get all the benefits of Ada
> object-oriented programming?
> 
> Like, what about:
> 
>     procedure A ( B: in access all T )

Should be:

procedure A ( B: access T )

and is Ok.
 
> or
> 
>     procedure A ( B: in out T )

Much better then using an acces type. 
 
> or
> 
>     procedure A ( B: in T )

Is like using "const&" in C++.

> Also, if I use access types, should I create new types or declare them
> directly in the procedure/function, and what about the 'all' access
> qualifier, should I create two types of access types (one with 'access'
> and one with 'access all'), or should I declare them directly in the
> procedure and decide individually what kind of access I need?

In Ada access type are not as often needed as in C++. So don't use then
unless you need them. References are done automatily by Ada.

If you know C++ then you will know about:

virtual void A (T& B); or virtual void A (T B);

As I said Ada will make the '&' Reference automaticly.

The "all" part is needed access to an object which have not been created
with "new". Using "all" for an access might reduce performace since the
compiler might have to do some extra checking on the access. Avoid if not
needed.

> I would like to program as cleanly as possible in Ada right from the
> start, so I'd be glad if someone could give me some hints. :-)

Hope I was of help.

You might also browse my Web page http://adacl.sourceforge.net. There are
lots of sources you can browse right on the web without downloading them.

With Regards.

-- 
mailto://krischik@users.sourceforge.net
http://adacl.sourceforge.net