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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: tagged record child: override constructor?
Date: Wed, 14 Sep 2005 11:28:40 +0200
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Date: 2005-09-14T11:28:40+02:00
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Ludovic Brenta wrote:
> Martin Krischik <krischik@users.sourceforge.net> writes:
> 
>>That's because all class members are virtual in Ada.
> 
> 
> I think this needs to be elaborated on.
> 
> All _primitive operations of a tagged type_ are _potentially_
> "virtual" in Ada.  Each caller of such a primitive operation decides,
> at the call site, whether the dispatching is static or dynamic.
> 
> In contrast, in (my recollection of) C++, all virtual methods dispatch
> dynamically from all call sites: the decision is not made at the point
> of call but at the point of definition of the method.

This is worth stressing. I was bitten by this distinction in cases like 
this:

type Blah is tagged ...;

procedure Do_Something (B : Blah); -- Default processing,
--  To be overriden/extended by descendant types.

procedure Run (B : Blah) is
begin
   ...
   Do_Something (B);
end Run;

If you make a descendant type (say Duh), the call inside Duh.Run will 
not be dispatching, but will call the Blah.Do_Something.

This is plain vanilla consequence of what you say, but for newcomers to 
Ada could be an easy mistake to made.

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