Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!umich!yale!cs.utexas.edu!uunet!mcsun!hp4nl!star.cs.vu.nl!jos
From: jos@cs.vu.nl (Jos Warmer)
Newsgroups: comp.lang.eiffel
Subject: Re: Eiffel cleanup #2: Doing away with void references
Message-ID: <5172@star.cs.vu.nl>
Date: 23 Jan 90 09:45:52 GMT
References: <227@eiffel.UUCP> <668@enea.se>
Organization: Fac. Wiskunde & Informatica, VU, Amsterdam
Lines: 26

In article <668@enea.se> sommar@enea.se (Erland Sommarskog) writes:
>
>You don't say it somewhere, but I suppose that
>
>   inherit NONE
>
>is illegal. Or does this mean that I inherit from every class in 
>the world? Computer telepathy? :-)
>
You are right, this is illegal.

The inheritance graph is a Directed Acyclic Graph (DAG) and because
NONE is a descendant from each class in the universe, no class can
be a descendant from NONE.
Note that this restriction is already defined within the current
eiffel definition, so no special case is needed for NONE.

                                 Jos Warmer
				 jos@cs.vu.nl
				 ...uunet!mcvax!cs.vu.nl!jos

PS. The compiler detects cycles in the inheritance graph and gives
    the following error message:

	Inheritance relation may not contain any cycles.
--