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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:

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.


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