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Subject: Re: [boost] [unordered] please don't allocate memory in the default constructor
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-24 15:44:15

Thorsten Ottosen wrote:
> Daniel James skrev:
> > The implementation also has to make sure the end iterator is valid for
> > empty containers. Currently the end iterator points to the sentinel
> > bucket so that the iterators don't need to be able to tell when
> > they've reached the end of the buckets, instead I'd have to use null
> > pointers for the end iterators and add a mechanism to detect when the
> > end of the buckets is reached - making iteration a bit slower. I'm not
> > sure if the trade off is worth it.
> Is it noticable slower?

You might also point the default constructed instance to a special, static bucket so the end iterator can refer to that. (Non-end iterators must compare equal against that special bucket, of course, once they advance far enough.) The check for empty is a check for a reference to that special bucket rather than to a null bucket pointer, or whatever. I won't begin to speculate on the performance (dis)advantage of this approach as I've not looked at any of the code.

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

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