Re: [boost] [Review] Xpressive

From: Eric Niebler (eric_at_[hidden])
Date: 2005-09-13 13:42:33

Thanks for the feedback. Comments inline ...

Fred wrote:
> (I didn't profile it, but it looked as though it would be
> extremely slow as a regex.)

If you ever do profile it, please post the results. I've dome some very 
limitted tests which show xpressive to be faster than Spirit, but I'd be 
very interested in real-world data.

> One thing that I'd like to see improved is the ability to organize complex
> regexes. I think one example that I hope is easy to implement would be an
> ability to name a set of characters. There are a number of literals (_d, _w,
> etc.) that already do this. I would have found it useful to be able to name
> my own character sets in static regexes. 

Good idea. Shouldn't be too hard to implement.

> The syntax cheat sheet should have a string literal added to it. I'd like to
> see it be complete, and this is the only thing I could find that wasn't
> there.

Noted.

> I'd like the documentation to better describe the _w identifier.

You're right. _w == (alpha | digit | '_'). I'll add it to the docs.

> On the page grammars_and_nested_matches.html, there is a discussion of how
> the library nicely handles all sorts different lifetime scenarios, but it
> does not discuss the lifetime of the regex refered to by a regex object that
> is refered to only through a “by_ref” clause in another regex. Does by_ref
> copy the object and manage the lifetime or not?

regex uses pimpl. by_ref() increments the impl's ref-count, so you never 
get dangling references. I'll make the docs more clear on this point.

> One big advantage of static xpressive regexes is the potential of making a
> complex regex relatively readable. I'd like to see some discussion of this
> in the docs. (Something along the lines of
> http://www.boost.org/libs/spirit/doc/style_guide.html) 

That would be useful.

> The documentation of ~as_xpr( character_constant ) should be included. This
> is a useful construct.

Yup, an oversight.

<snip>

> (I also broke my personal record for long error messages. Even Spirit has
> never generated a 10MB error message for me before!)

I consider unreasonably long error messages to be bugs in xpressive. 
Anybody encountering such an error should send me a bug report, and I'll 
see about adding a static assertion to give a better error message.

> 	* Do you think the library should be accepted as a Boost library? Be
> sure to say this explicitly so that your other comments don't obscure your
> overall opinion.
> Yes. 
> 

Thanks for taking the time.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com