Re: [boost] [Review] xpressive

From: Eric Niebler (eric_at_[hidden])
Date: 2005-09-16 10:44:20

Daryle Walker wrote:

> On 9/15/05 1:10 PM, "Eric Niebler" <eric_at_[hidden]> wrote:
>
>>  In practice, the only reason why you might iterator over
>
>>  all sub-matches is to print them out. Otherwise, the sub-matches are 
>
> accessed
>
>>  randomly, because (for example) the 1st sub-match is a date and the 3rd
>>  sub-match is an email address, and I'm not interested in the 2nd. See?
>
>
<snip>

>
> It looks like the current setup is not STL-friendly. Most of the "what"
> list is one type of thing, the in-order pieces of the regex parse. The
> first item of the list doesn't match that pattern (since it's the whole
> parse). I'm guessing that this "old" way wasn't a problem because people
> expected 1-based arrays, so the 0-index could be special. That doesn't 
> work
> in a 0-based array culture, like C++ (or C). C++ people would expect the
> 0-index element to match the general rule of the list. This mixing of
> element types mixes concerns (violating "keep it simple, silly"). A
> STL-friendly alternative would to have separate member functions for the
> whole-parse and the list-of-parse-pieces, then have a special function
> (member or non-member) that generates a regex-culture combined list.
>

I agree, if we we're only concerned about satisfying people familiar 
with C++ culture. But we are also trying to satisfy people familiar with 
regex culture. Every regex package out there I know of that supports 
back-references begins numbering captures at 1. I don't know why. But I 
do know that to break with that tradition now would cause massive 
confusion. Besides, I'm trying to minimize the differences between 
xpressive's interface and TR1 regex.

Is it a wart? OK, I agree. But frankly, I don't feel that this is an 
ugly enough wart for me to break with established practice.

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