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From: jr@hpgnd.grenoble.hp.com (Jean-Ren BOUVIER)
Newsgroups: comp.lang.c++
Subject: How to define a List class
Message-ID: <350001@hpgnd.grenoble.hp.com>
Date: 3 Jun 91 15:07:44 GMT
Organization: Hewlett-Packard, GND
Lines: 37

I'm looking for ideas in the classical area of "list"  packages.  I want
to define a "List" class which could be the base class of other  objects
so that these could then be put on linked lists.

In a more C++-ish way, I'd like to have the following:

	class List {
	// details
	List	*next;	// I also accept solutions with "next" defined
			// as a (virtual) function.
	};

	class SomeListableObject: public List /* may have other parents */ {
	// details
	};

	// a few lines later ...
	SomeListableObject	*list;
	// ...
	// assignment to list
	// ...
	while(list) {
		// do something
		list	= list->next;
	}

I DON'T want to  consider  solutions  based on  templates  (List<Object>
types) or generic classes - as I don't want to replicate code.

My problem is that "next" holds (or returns) a pointer to a List, not to
a  SomeListableObject,  i.e.  the above  code  won't  compile,  unless I
introduce a cast like:

	list	= (SomeListableObject*)list->next;

Is there a solution  that  avoids  that cast and which  doesn't  use the
preprocessor ?