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From: ogden@seal.cis.ohio-state.edu (William F Ogden)
Newsgroups: comp.lang.eiffel
Subject: Re: Reference Semantics
Message-ID: <1991Jun21.215959.13966@cis.ohio-state.edu>
Date: 21 Jun 91 21:59:59 GMT
References: <1991Jun12.072557.7282@jyu.fi> <133644@tut.cis.ohio-state.edu> <1991Jun19.001829.28317@syacus.acus.oz.au>
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In article <1991Jun19.001829.28317@syacus.acus.oz.au> ian@syacus.acus.oz.au (Ian Joyner) writes:
   ...
>>the analogy suggests strongly that we examine very carefully whether
>>the visible use of references is really that central to object oriented
      ^^^^^^^
>>design. A good example or two ...

>                      ...          Take networking and databases, where
>shared information is what the customer wants. The user may want fast
>access to some information, and therefore have their own copy, or alias.
>But this has the danger that their information gets out of date. If
>slightly out of date information is acceptable then this is OK. If it
>is not acceptable, then the user must always access the original by
>means of a reference.

A database is surely a shared resourse in a system, but it's not so
clear that clients should share access to subcomponents of it via
visible references. Generally, if several clients are using mutually
referenced information as if it were private, you're going to have
big problems.
It is not my impression that the database community has really resolved
the problem of achieving high performance while providing safe, functionally
adequate access to a database. So it's unclear that this is a good basis
for an example of where visible reference semantics is the obvious solution.

>As object oriented programming reflects the real world, it seems that
>references will be inevitable.

At the risk of getting back into those dangerous analogies, note that
referencs semantics really entail multiple larger objects routinely sharing
possesion of smaller objects. For very good reasons, this rarely happens
in the real world. Imagine, for example, several people in a room each
possesing a remote tuner for the room's only television set. The chaos
that would normally result makes it clear why we avoid such situations in
the real world, and by analogy why we would be prudent to do so in our
programming world.