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From: horstman@mathcs.sjsu.edu (Cay Horstmann)
Newsgroups: comp.lang.c++
Subject: Borland language extension virtual function = [ ... ];
Message-ID: <1991Jun27.130247.5107@mathcs.sjsu.edu>
Date: 27 Jun 91 13:02:47 GMT
Organization: San Jose State University - Math/CS Dept.
Lines: 41

I just attended a product presentation by a Borland guy on their class
library for Microsoft Windows called ObjectVision. I was somewhat distressed
to see an odd construct 

	class MyWindow : public TWindow
	{	// ...
	public::
		virtual void paint() = [ WM_START + WM_PAINT ];
		// ...
	};

(I am quoting from memory, so the details may not be correct 100%). The idea
is that the paint() function would be selected when the WM_PAINT message is
sent from MS Windows. 

They have a fancy name for this, dynamic message dispatching. 

Did anyone see this before? Supposedly it is supported in BCC 2.0. Is the
mechanism really tied to MS Windows, or does it something useful in a 
general construct?

The speaker (I believe the project head for ObjectVision--can't remember
his name) insisted that this did not violate any C++ standard, being "merely"
an extension. To me, this sounds like utter nonsense. Assuming for the moment
that the feature is indeed closely tied to Windows (or maybe other event-
driven UI that use small integers as message ID's), one of two things will
happen:
    Nobody else will support it, and Borland C++ (otherwise an admirable 
    product) will be on the route that killed Pascal, with proprietary
    extensions in every implementation.

    Every DOS vendor must support it to stay compatible, and Borland manages
    to place a true wart into the de facto language without even bothering
    to go through the ANSI committee. 

Maybe other netters have more info on this. My impression that the speaker
was an evil person was amplified when, upon his question what Borland could
do for us, I told him "Improve the Usenet support", and he answered "The
what?". 

Cay