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From: jcm@mstr.hgc.edu (James McKim)
Subject: Re: Functions without side effects (was Old confusion)
Message-ID: <1991Jun17.141842.25702@mstr.hgc.edu>
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Organization: The Hartford Graduate Center, Hartford CT.
References: <130242@tut.cis.ohio-state.edu> <1991Jun5.072556.19870@irisa.fr> <1991Jun5.083241.13145@tkou02.enet.dec.com> <956@puck.mrcu> <1186@tetrauk>
Date: Mon, 17 Jun 91 14:18:42 GMT

In article <1186@tetrauk.UUCP> rick@tetrauk.UUCP (Rick Jones) writes:
>
>Wait for Eiffel version 3! (not long now, I hope).

Second that (e)motion! And where/how can I get the latest 
_Eiffel: The Language_ ASAP?

>  It will support a construct
>"strip" which means "the attributes of this object, except for <the parameters
>given to strip>".  If there are no parameters, it is all the attributes.  Then
>the postcondition "strip = old strip" means "no change".  Since strip allows
>you to explicitly omit specified attributes, you can write a postcondition
>which means "no change to any attributes except those specified".  So by
>omitting attributes which only affect internal state, the postcondition can
>ensure that the important things are unchanged, even though the internal state
>may have been modified.
>
Hmmm. Is "strip" included in the public interface? Offhand, it seems it
should _not_ be since, if I understand correctly, it may include parameters
that are private attributes. These the client does not need/want to see
and, besides, the public interface should not change if I change the
name of a private attribute. Also "strip" wouldn't help with public 
attributes that change, since the client needs to know _how_ each
such attribute changes, not just which ones may. It _does_ look like
a very useful compiler directive, though....
>-- 
>Rick Jones, Tetra Ltd.  Maidenhead, Berks, UK		rick@tetrauk.uucp
>Chairman, NICE (Non-profit International Consortium for Eiffel)
>
>Any fool can provide a solution - the problem is to understand the problem

-- Jim

*------------------------------------------------------------------------------*
Jim McKim  (203)-548-2458   _Give_ people fish and they eat for a day.  
Internet:  jcm@mstr.hgc.edu _Teach_ people to fish and they eat for a lifetime.