Re: [boost] [unordered] please don't allocate memory in the default constructor

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  http://www.sig.com

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