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From: diamond@jit533.swstokyo.dec.com (Norman Diamond)
Newsgroups: comp.lang.eiffel
Subject: Re: Reference Semantics
Message-ID: <1991Jun13.074318.337@tkou02.enet.dec.com>
Date: 13 Jun 91 07:43:18 GMT
References: <131691@tut.cis.ohio-state.edu> <1181@tetrauk.UUCP> <133154@tut.cis.ohio-state.edu> <1991Jun12.072557.7282@jyu.fi>
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Reply-To: diamond@jit533.enet@tkou02.enet.dec.com (Norman Diamond)
Organization: Digital Equipment Corporation Japan , Tokyo
Lines: 35

In article <1991Jun12.072557.7282@jyu.fi> sakkinen@jyu.fi (Markku Sakkinen) writes:
>In article <133154@tut.cis.ohio-state.edu> ogden@seal.cis.ohio-state.edu (William F Ogden) writes:
>>In article <1181@tetrauk.UUCP> rick@tetrauk.UUCP (Rick Jones) writes:
>>>Pointers in C do cause problems, and we have the experience of that,
>>>                                                                  but it is
>>>very easy to make a lot of mistakes in C with pointers because the language
>>>doesn't help you handle them properly.  References in an OOPL are a whole
>>>different issue.
>>
>>Somehow I'm getting this deja vu sensation that we're back in the late 60's
>>discussing Go To's. One side is saying that Go To's (object references) have
>>an excessively complex semantics which can easily lead to programming errors.
>
>I think that the need to share some objects is much more fundamental
>for object modelling than is the need to jump for imperative programming.
>The (visible) use of references should be restricted to a minimum,
>but accepted without remorse whenever it is necessary.

I agree with that conclusion, but think that the reasoning and application
are backwards.  Sharing and aliasing are sometimes necessary and should be
kept to a minimum, yes.  I think the sharing and aliasing should be visible,
so that readers will know what to expect.  The invisible aliasing generated
by reference semantics is worse than a label that is a target of multiple
gotos.  An object gets changed when the user didn't expect it, and has to
do a lot of tracing to find out where....

Part of the problem with C pointers is that they are overused and abused
as a result of C's treatment of arrays.  (A garbage collection in C can be
declared with [].)  A fairer comparison would be Pascal-style pointers (or
even PL/I-style pointers) vs. the invisible sharing generated by reference
semantics.
--
Norman Diamond       diamond@tkov50.enet.dec.com
If this were the company's opinion, I wouldn't be allowed to post it.
Permission is granted to feel this signature, but not to look at it.