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From: minow@bolt.enet.dec.com (Martin Minow)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How does Symantec implement inheritance?
Message-ID: <20433@shlump.nac.dec.com>
Date: 21 Feb 91 22:02:23 GMT
Sender: newsdaemon@shlump.nac.dec.com
Distribution: usa
Organization: Digital Equipment Corporation
Lines: 51


In article <1991Feb20.205941.5105@iitmax.iit.edu>, soudan@iitmax.iit.edu
(Bassel Soudan) asks about multiple inheritance under the Think Class
Library.

Since the compiler doesn't support multiple inheritance, you either
need to write your own or take some other application-specific
action.  For example, CStaticText is a descendent of CPanorama, but
adds some methods that are data-specific (SetTextHandle, for example)
and others that are command-specific.

Another useful method is to split the task into two (or more) separate
classes that are linked together by reference instance variables,
following the philosophy behind CScrollPane and CPanorama.  For example,
I wrote a ListManager analog that consisted of two classes,
	struct ListSelector : CList {
	    CSelector		*itsSelector;

	    void		IListSelector(void);
	    void		InstallSelector(
		CSelector	    *aSelector
	    );
	    PRIVATE void	AdjustSelector(void);
	    void		ChangeSelection(
		short		    aSelection
	    );
	    void		Add(
	 	CObject		    *anObject
	    );
	    /* etc. */
	}
and
	struct ListPanorama : CSelector {
	    long		itsDoubleClickCmd;

	    void		IListPanorama(
		... boring CSelector/CPanorama parameters ...
	    );
	    void		Draw(...);
	    void		HiliteItem(...);

The CSelector contained the visual and command hierarchies, while
the ListSelector contained the data.  When objects are added
or removed from the list, the method calls AdjustSelector which
adjust the CPanorama's bounds.  A slightly buggy source file was
posted to the Think-C mailing list a few weeks ago.  (send mail
to think-c-request@ics.uci.edu to join).

Good luck - hope this isn't too confusing.

Martin.