Re: [boost] [regex] Support for Perl's (*SKIP)

Subject: Re: [boost] [regex] Support for Perl's (*SKIP)
From: Sei Lisa (seilisasl_at_[hidden])
Date: 2015-04-19 12:57:06

John Maddock wrote, On 2015-04-19 12:55:
> 
> I've added a bug report for this:
> https://svn.boost.org/trac/boost/ticket/11205

Thank you very much.

> However, in the mean time, there is a much simpler workaround, if you use:
> 
>   (?x-s)                 (?# free spacing, dot doesn't match newline)
>   (?://.*+               (?# eat single-line comment text)
>     |/\*[\S\s]*?\*/      (?# eat multi-line comment text)
>     |"(?:\\.|[^"\n])*+"  (?# eat string text)
>   )                      (?# skip these)
>   |\b(foo)\b             (?# match this)
> 
> And if $1 matched, then you have what you were looking for, otherwise
> discard.  It's not as "neat" as the original, but is no less/more
> efficient.

Isn't that basically the same that I said, just changing the grouping?

>> Without (*SKIP), it can be done only by calling regex::search
>> multiple >> times, using an expression like this:
>>
>>    (?-s)//.*+|/\*[\S\s]*?\*/|"(?:\\.|[^"\n])*+"|(\bfoo\b)
>>
>> and ignoring every match where group 1 wasn't matched. That's
>> presumed to be slower, and certainly more inconvenient for the
>> programmer.

The match shouldn't be given up if a comment or string is found; the
programmer needs to keep searching until either there's no match, or
group 1 is matched. It's what I ended up doing.

I presumed it would be less efficient because it's creating an
additional match group per call, and because there's the set-up time and
function call overhead over the multiple calls that are necessary this
way. And not sure but it's possible there are more cache misses.

Sei