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From: jkanze@otelo.ibmmail.com
Subject: Re: string/cow/algorithm
Date: 1998/08/13
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In article <6qo3fq$dum$1@pigpen.csrlink.net>,
  jpotter@falcon.lhup.edu (John Potter) wrote:
>
> The original question was the conformance of a string class which
> sorted the original string when a copy was sorted.  The answer was
> that the FDIS is different from the CD2 and the implementation is not
> conformant.  A following question asked about making a cow string
> class conformant.
>
> On writing a standard conformant string class.
>
> AllanW@my-dejanews.com wrote:
>
> : I think that using a proxy class should handle this fairly well
>
> Sorry.  Unless this has also changed from the CD2, it is required that
> string::operator[] return a T& and that string::iterator::operator*
> return a T&.  Proxies are expressly forbidden by these requirements.
>
> Perhaps one of the reasons that SGI decided against reference counting
> for their string as you indicated.

I thing that the problem was more linked with thread safety.  However, th=
e
requirement you just mentioned does make it more difficult (and less of
a win).

> But Mark wants to write a standard conformant reference counted cow
> string class.  Let's not tell him not to do it but offer some help in
> doing it.
>
> My interest was in what I can expect from a conformant string and that
> has been satisfied.  However, I am interested in any standard
> conformant techniques that may help Mark do a better job than the
> little relayed information which I posted.  Or maybe there are no
> better techniques.

I didn't see what has been posted, but basically, you have to isolate
(unshare) and lock (prevent further sharing) anytime you take non-const
reference or iterator.  The lock must be maintained until the next action
which invalidates the iterator.

--
James Kanze    +33 (0)1 39 23 84 71    mailto: kanze@gabi-soft.fr
        +49 (0)69 66 45 33 10    mailto: jkanze@otelo.ibmmail.com
GABI Software, 22 rue Jacques-Lemercier, 78000 Versailles, France
Conseils en informatique orient=E9e objet --
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