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Re^2: regex anchoring issue

by smls (Pilgrim)
on Feb 15, 2013 at 11:23 UTC ( #1018879=note: print w/ replies, xml ) Need Help??


in reply to Re: regex anchoring issue
in thread regex anchoring issue

Why do you place the regex in a (?>...) non-backtracking group?


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Re^3: regex anchoring issue
by kcott (Abbot) on Feb 16, 2013 at 05:58 UTC

    Wrapping regexp alternations in (?>...) is something I do by default. While there may be rare cases where this might be problematical, I haven't encountered any: it's something that doesn't hurt and, indeed, often helps.

    This usage is based on a "Perl Best Practices" guideline: Backtracking (page 269). It's summarised on page 271 as:

    ... rewrite any instance of:

    X | Y

    as:

    (?> X | Y )

    While I'm not a slave to all "Perl Best Practices" guidelines, this is one I have found to be useful.

    Update: s/have encountered/haven't encountered/

    -- Ken

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