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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Question about OO programming in Ada
Date: Mon, 08 Dec 2003 10:34:47 +0100
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Date: 2003-12-08T10:34:47+01:00
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On Mon, 08 Dec 2003 08:42:28 GMT, Hyman Rosen <hyrosen@mail.com>
wrote:

>Chad Bremmon wrote:

>> Because Ada 95 is strongly typed, the compiler can figure out at compile 
>> time which function to call, based on the type.  This ensures that 
>> dispatching is done during compile time.  You still have the look and 
>> feel of polymorphism, without the non-deterministic nature of runtime 
>> dispatching.
>
>What makes you think that C++ is any different in this regard?

C++ does not distinguish class-wide and specific types. The same
object is treated as a class-wide or specific depending on the
run-time call context. For example:

class X 
{
public :
   virtual void Foo ();
   virtual void Baz ()
   {
      Foo ();
   }
   ...

Is the call to Foo from Baz dispatching? The answer is, well,
sometimes it will. Arguably C++ is not strongly typed because no type
could be addressed to implicit "this" in Baz, and so to the actual
type [*).

In Ada one can always statically determine whether a call is
dispatching. Unfortunately, this advantage remains largely unused
because of redispatching support and embedded tags.

-------
[*]  "this" is a class-wide pointer when Baz was not directly or
indirectly called from a constructor/destructor. It is a specific
pointer otherwise.

--
Regards,
Dmitry Kazakov
http://www.dmitry-kazakov.de