Re: [Boost-users] [xpressive] Using it with input iterators or how far the backtracing will go back

On 11/9/2010 3:03 AM, Eric Niebler wrote:

(cross-posting to spirit-devel)

On 11/8/2010 12:36 PM, Alex Dubov wrote:

...

Nat Linden writes:

...

Once upon a time, the Serialization library came with backtracking input iterators used to parse XML input files with Spirit. I briefly glanced over more recent Serialization documentation without spotting them. Do they still exist?

Yes, in a way. Spirit only requires forward iterators, not bidi ones, like xpressive. Input iterators can be adapted to become forward ones in a fairly straightforward way, and indeed, spirit has a customizable multi_pass iterator adapter to do just that.

Up until now I thought spirit to be an overkill for my stuff, but I'm considering using it now.

Just hazarding a guess here, but the multi_pass_iterator probably works by caching all the read data so far. Otherwise, how would it support making a copy of the begin iterator and dereferencing it at a later point in time? If that solution wasn't good enough for you before, you probably don't want multi_pass_iterator+Spirit.

Can the Spirit guys chime in on this?

The multi_pass iterator uses a sliding window that can be flushed when you reach a deterministic point, a point of no return where back-tracking is no longer an option. In this case, saved iterators are invalidated. Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net