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Re: Re: Passing $2 to a sub

by the_slycer (Chaplain)
on Feb 13, 2001 at 23:13 UTC ( #58199=note: print w/replies, xml ) Need Help??


in reply to Re: Passing $2 to a sub
in thread Passing $2 to a sub

I may be wrong (I've only read Mastering Regular Expressions once), but doesn't using $&, $' or $` anywhere in your program cause some fairly severe performance issues?

Looks like the regex originally used should work - just trying to print $_ instead of $_[0]

Replies are listed 'Best First'.
Re: Re: Re: Passing $2 to a sub
by MeowChow (Vicar) on Feb 13, 2001 at 23:28 UTC
    Yep, you are right. From perlre:
    WARNING: Once Perl sees that you need one of $&, $`, or $' anywhere in the program, it has to provide them for every pattern match. This may substantially slow your program. Perl uses the same mechanism to produce $1, $2, etc, so you also pay a price for each pattern that contains capturing parentheses. (To avoid this cost while retaining the grouping behaviour, use the extended regular expression (?: ... ) instead.) But if you never use $&, $` or $', then patterns without capturing parentheses will not be penalized. So avoid $&, $', and $` if you can, but if you can't (and some algorithms really appreciate them), once you've used them once, use them at will, because you've already paid the price. As of 5.005, $& is not so costly as the other two.
       MeowChow                                   
                   s aamecha.s a..a\u$&owag.print

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