From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,HEADER_SPAM,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,b30bd69fa8f63cb2
X-Google-Attributes: gid103376,public
X-Google-Thread: fc772,b30bd69fa8f63cb2
X-Google-Attributes: gidfc772,public
X-Google-ArrivalTime: 2003-06-23 08:49:21 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!uwm.edu!rpi!not-for-mail
From: brangdon@cix.co.uk (Dave Harris)
Newsgroups: comp.lang.ada,comp.lang.c++.moderated
Subject: Re: C bug of the day
Date: 23 Jun 2003 11:51:31 -0400
Organization: unknown
Sender: cppmods@netlab.cs.rpi.edu
Message-ID: <memo.20030623120917.135A@brangdon.madasafish.com>
References: <J6jJa.13112$KF1.276346@amstwist00>
Reply-To: brangdon@cix.co.uk
NNTP-Posting-Host: netlab.cs.rpi.edu
X-Original-Date: Mon, 23 Jun 2003 12:09 +0100 (BST)
X-Submission-Address: c++-submit@netlab.cs.rpi.edu
X-Auth: PGPMoose V1.1 PGP comp.lang.c++.moderated
	iQBVAwUAPvch/0HMCo9UcraBAQF1VQIAiMSD7QhMrZq5rGHLPhmsCcJuiGEqL/54
	REArhBsv7EGZwufVwOsXQ9jOAlHDuudif7fT0/VSBEP+T2IUnJemWw==
	=6R3Q
Xref: archiver1.google.com comp.lang.ada:39609 comp.lang.c++.moderated:68992
Date: 2003-06-23T11:51:31-04:00
List-Id: <comp.lang.ada>

tslettebo@chello.no.nospam (=?Windows-1252?Q?Terje_Sletteb=F8?=) wrote 
(abridged):
> > (GC is a big win when objects can be shared by pointers which are
> > encapsulated. Then the question, "Has everyone finished with this
> > object?" gets replaced by "Have I finished with this pointer?",
> > which is a more local, encapsulated issue - fundamentally easier.)
> 
> You get something similar with reference-counted smart pointers.

Yes. Which have well-known problems with loops.

Also, these introduce some of the issues you complain about for GC. For 
example, you may need weak pointers (eg boost has a weak pointer class).


> > This would be a criticism of Java, not GC. Most GC languages have
> > idioms to encapsulate stack-based cleanup. (These are often based
> > on closures.) RAII is only "usual" in C++.
> 
> In what way does this differ from RAII in C++. Could you give an
example
> from one of those languages?

In Smalltalk:

    File open: 'filename' do: [:file| "use file" ]

The stuff in square brackets is a block closure. #open:do: is a message 
sent to File, which opens the file, evaluates the closure, then closes
it 
again. So this is roughly equivalent to:

     {
         File file( "filename" );
         // use file
     }

#open:do: could be defined (on class File) like:

     open: aString do: aBlock
         |file|
         file := self open: aString.
         ^[aBlock value: file] ensure: [file close]

where #ensure: is like try/finally in Java.

-- Dave Harris, Nottingham, UK

      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated.    First time posters: Do this! ]