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Subject: Re: [boost] [xint] Third release is ready, requesting preliminary review
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-05-03 13:40:18

Chad Nelson wrote:
> On 05/03/2010 12:46 PM, Stewart, Robert wrote:
> >> Not exactly useless -- I *do* know enough to avoid things that are
> >> completely useless. :-) The purpose was to initialize them to the
> >> value of another integer, such as a parameter, before going into a
> >> loop that modifies them based on their current values. With
> >> copy-on-write, the initial allocation can be skipped, which
> >> (depending on the number of times it needs to loop) can be a
> >> significant savings.
> >
> > You say you copy an instance and then mutate it. Guess what! The
> > copy involves manipulating the reference count and the mutating
> > operations must all check whether the instance is unique. The first
> > mutating operation actually makes a unique copy and the rest just
> > check superfluously.
> The first operation *may* make a unique copy, if the operation results
> in a change to the number. There's no guarantee that it will.

Yes, in that case COW prevents premature allocation/copying, but that's not how you phrased the example originally.

We've been arguing at cross-purposes, apparently.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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