Xref: utzoo comp.lang.eiffel:1686 comp.object:3776
Newsgroups: comp.lang.eiffel,comp.object
Path: utzoo!utgpu!cunews!knight
From: knight@mrco.carleton.ca (Alan Knight)
Subject: Re: Reference Semantics
Message-ID: <1991Jun22.175434.21450@cunews.carleton.ca>
Sender: news@cunews.carleton.ca
Organization: Carleton University, Ottawa, Canada
References: <133644@tut.cis.ohio-state.edu> <1991Jun19.001829.28317@syacus.acus.oz.au> <1991Jun21.215959.13966@cis.ohio-state.edu>
Date: Sat, 22 Jun 1991 17:54:34 GMT

In article <1991Jun21.215959.13966@cis.ohio-state.edu> ogden@seal.cis.ohio-state.edu (William F Ogden) writes:
>In article <1991Jun19.001829.28317@syacus.acus.oz.au> ian@syacus.acus.oz.au (Ian Joyner) writes:
>   ...
>>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.

  The phrase "larger objects ... sharing possession of smaller
objects" implies a physical part-of relationship, sharing of which
doesn't often happen in the real world.   That doesn't mean that
objects aren't shared.
  In fact, in the "real" world that I live in, objects are usually
shared, and copying is fairly rare.  At my house, we have one
television set which is shared between all the residents.  It's true
that there's only one remote control, but if my wife decides to change
the state of the television set, it certainly affects the copy that
I'm referencing.
  Copying semantics (in which as soon as I walk into the room I get my
own television to look at) would be rather disconcerting.
Copy-on-write would be rather entertaining, if anyone who changed the
channel got a new television set.  I'd soon be able to open my own
electronics store.  I'm not sure what would happen to the reference
to the TV from the bookcase it sits on, though.  We might need to
clone quite a bit of stuff.

  To actually make a point:  The real world has state and reference
semantics all over the place.  There may be good arguments for
avoiding them, but the claim that they are not used in the real world
is not one of them.


-- 
--
  Alan Knight   knight@mrco.carleton.ca  +1 613 788 5783   Support
  Dept. of Mechanical and Aeronautical Engineering         the
  Carleton University, Ottawa, Ontario, Canada, K1S 5B6    LPF