Re: [boost] [xint] Third release is ready, requesting preliminary review

Subject: Re: [boost] [xint] Third release is ready, requesting preliminary review
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-05-03 07:39:09

Chad Nelson wrote:
> On 05/02/2010 04:19 PM, Jeffrey Lee Hellrung, Jr. wrote:
>
> > If something's not going to be modified, you might as well
> > make it a constant reference.
>
> I assume the savings come from somewhere else, since
> I already use constant references wherever I can get away with it.
>
> > The only example I can think of where COW might come in
> > handy is if you do something like
> >
> > cow* p_x1 = new cow();
> > cow* p_x2 = new cow(*p_x1); // no deep copy / shared ownership
> > // ... [A] Read from *p_x1, maybe? ...
> > delete p_x1; // *p_x2 now has exclusive ownership
>
> If I read your example correctly, then that's about what I
> was thinking
> of: algorithms that have to start with a copy of one or more of the
> passed-in parameters, but then need to modify it/them. The division
> algorithm requires this, just as one example off the top of my head.

If your algorithm requires a copy, then COW should make it slower because it will first manipulate the reference count and because you must query in each mutating operation whether to make a unique copy.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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