Newsgroups: comp.lang.smalltalk
Path: cantaloupe.srv.cs.cmu.edu!nntp.club.cc.cmu.edu!hudson.lm.com!newsfeed.pitt.edu!gatech!howland.reston.ans.net!ix.netcom.com!netcomsv!uu3news.netcom.com!netcomsv!uucp3.netcom.com!slcgate!servio!news
From: cohenb@slc.com (Bruce Cohen)
Subject: Re: Anyone implemented Futures in VisualWorks 2.0?
In-Reply-To: knight@mrco.carleton.ca's message of Sat, 18 Mar 1995 18:29:22 GMT
Message-ID: <COHENB.95Mar21171347@topdog.slc.com>
Lines: 33
Sender: news@slc.com (USENET News)
Nntp-Posting-Host: topdog
Reply-To: cohenb@slc.com
Organization: Servio Corporation
References: <peter_korp-1603951124430001@groomlake.dis.anl.gov>
	<16MAR199515551864@pavo.concordia.ca> <3kebdp$3lq@mc1.mcnet.ch>
	<knight.795551362@tina.mrco.carleton.ca>
Date: 22 Mar 1995 01:13:47 GMT

In article <knight.795551362@tina.mrco.carleton.ca> knight@mrco.carleton.ca (Alan Knight) writes:
>>    It depends on your implementation. ParcPlace uses an extra layer
>>    of indirection in all their object references. This allows a cheap
>>    and quite easy become: operation (although there's more fiddling
>>    with the garbage collector than just switching two references)
>> 
>>    Digitalk, which I think Charles is talking about, uses direct object
>>    references. This is faster in general, but makes become: an extremely
>>    expensive operation (and one-way instead of two-way). I've also heard
>>    that become: can be unreliable in some Digitalk implementations.

IBM Smalltalk, on which VisualAge is built, also implements a one-way
become.  The method comment for Object>>become: says that an
implementation might implement either one-way or two-way and that you
should conservatively expect one-way.  In fact, one-way is what I see in
the Windows version of VisualAge 2.0
-----------------------------------------------------------------------------
"Only a proper understanding of the constraints imposed by the
properties of our space and of the rich repertoire permitted within
these constraints allow the achievement of a balanced disciplined
freedom."  - Arthur Loeb in "Concepts and Images"
-----------------------------------------------------------------------------
Bruce Cohen, Servio Corporation                  |   email:  cohenb@slc.com
15400 NW Greenbrier Pkwy, Suite 280              |   phone: (503)690-3602
Beaverton, OR USA 97006                          |   fax: (503)629-8556
-- 
-----------------------------------------------------------------------------
"Designers are pretty bright people, however.  They can come up with a
plausible-sounding example for almost anything." - Donald Norman
-----------------------------------------------------------------------------
Bruce Cohen, Servio Corporation                  |   email:  cohenb@slc.com
15400 NW Greenbrier Pkwy, Suite 280              |   phone: (503)690-3602
Beaverton, OR USA 97006                          |   fax: (503)629-8556
