Re: Fusion-ifying proto parse trees

David Abrahams wrote:
> "Eric Niebler" <eric@xxxxxxxxxxxxxxxxxxxx> writes:
>
> > Every time you increment a joint view iterator, you're checking to see
> > if you've reached the end of the first sequence, so you know when to
> > start the second. And if Iterator::first_type is itself a joint view
> > iterator, it *also* must check to see if it's at the end of *its*
> > first sequence to know if it should start its second. And so on. If
> > you do a bunch of push_backs and end up with a joint_view of a
> > joint_view of a joint_view, iterating it will be far from
> > trivial. This sort of flattening-on-the-fly is *exactly* the problem
> > that non-segmented proto has, and is the problem that segmented
> > iterators solve.
>
> Just to be clear, this is all compile-time cost.  There's no reason
> *that* has to be slow at runtime.

Definitely. But I think I see Eric's point. Anyway, that's easy enough
to test. I still have some reservations with the Zero-copy expression
template construction because in my experience holding references
in many cases actually slow things down compared to holding just
the values, especially for trivial elements like chars.

Regards,
--
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net



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