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From: ssimmons@convex.com (Steve Simmons)
Newsgroups: comp.lang.c++
Subject: Passing a doubly dereferenced pointer of a base class
Message-ID: <ssimmons.667577980@convex.convex.com>
Date: 26 Feb 91 14:19:40 GMT
Sender: news@convex.com (news access account)
Organization: Convex Computer Corporation, Richardson, Tx.
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	I've run across the following problem for defining an interface
	for a base class.  Essentially, I need to create a function 
	with the following behavior....

		int BaseClass::function(BaseClass** parm);

	The problem is that there in an intention to derive other classes
	from this base class.  Therefore, if I were to make the following
	declaration...

		class DerivedClass : public BaseClass {} 

		DerivedClass *instance;

	I would need to make the following cast in the call to the 
	inherited member...

		instance->function((BaseClass**) &instance);

	In fact, I cannot even use this base class as part of 
	a multi-inherited chain... Is there a decent work around
	so that this cast is not necessary???  Is it a weakness in 
	the language??? I've noticed that the NIH uses a castdown
	mechanism and is this the best that we can do??? 

	Thank you. 

						Steve Simmons