Re: [boost] [fusion] segmented sequences [ was Re: [fusion] ftag ]

From: Andy Little (andy_at_[hidden])
Date: 2006-09-25 20:09:51

"Joel de Guzman" <joel_at_[hidden]> wrote in message 
news:ef9mui$nhb$1_at_sea.gmane.org...

> You mean: fusion should not copy the compile time behavior at runtime?
> Hmmm... but of course it does not. Let me get this straight: push_back
> *IS* cheap. It is the unfolding (iterating over) the push-backed view
> that is less than ideal. This can be made efficient by segmented
> techniques.

Yes It is the construction of a joint_view with N+1 elements from a joint view 
with N elements. The compiler (VC8) seemed to be copying the stuff from the 
first to the second, and so on for each bigger iteration of joint view right up 
to the 16 element version. I don't think it would see much of what it had 
originally once it had got through all that copying, but It would need better 
analysis than I gave to say for sure, but there seemed to be quite a few traces 
of calls to joint view ctors in the final output, and  I didnt like the look of 
it.

regards
Andy Little