Re: [boost] xpressive and white space skipping

From: Dave Jenkins (david_at_[hidden])
Date: 2007-11-23 16:16:35

"Jorge Lodos Vigil" <lodos_at_[hidden]> wrote in message 
news:ECBF993526E3BC47BD232BDC77D6933706A916F5E6_at_mercurio.segurmatica.cu...
> I have to thank you again, this is a better solution than the prepocessing 
> I was thinking about. This solves our problem. The only caveat is that 
> proto is not yet a boost library, but I hope this will imply just a header 
> change when definitely accepted and BOOST_PROTO_AUTO will not change.
> So far you came with 2 different ideas, the first one modifying the way we 
> traverse the sequence, now an elegant way of modifying the grammar. There 
> is still the alternative of modiying the algorithm to use an additional 
> skip regex. I wonder, performance wise, what should be the best option for 
> arbitrary texts? Do you (or someone else) could shed some light on this?

If you're worried about using Proto, you could use:

    regex_skip skip_spaces = nil[check(&not_space::enable)];
    regex_skip normal = nil[check(&not_space::disable)];

instead of:

    BOOST_PROTO_AUTO( skip_spaces,  nil[check(&not_space::enable)] );
    BOOST_PROTO_AUTO( normal, nil[check(&not_space::disable)] );

They do the same thing.  I've just found BOOST_PROTO_AUTO is faster for 
small, nested regexes where you're not interested in the match info.

As for performance, I don't know how a modified algorithm would compare with 
the modified iterator that I used.  I presume you are thinking about 
something like icase (which ignores case), but that ignores spaces.  Maybe 
Eric can answer that one.