[Melbourne-pm] Just how much does $& slow things down?

Toby Corkindale toby.corkindale at strategicdata.com.au
Thu Nov 20 19:31:38 PST 2008

Alfie John wrote:
>  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.
>     This is the only place in the whole program which uses a regex, so
>     the impact on other parts of the program should be nil.
>     I just don't know if it's going to be worth removing those
>     references to $&, and how much it will benefit the running of the
>     program.
>     Obviously, the bigger @an_array is, the larger the impact, but I can
>     safely say it won't be much bigger than about 50.
>     So, are we talking an order of magnitude slower? More? Less? Anybody
>     even want to take an educated guess?
> In other words, having it only in the above code will still impact *all 
> other* regexes in any code, including all imported modules.

Do you have to use $&, or can you use ${^MATCH} instead? (Which doesn't 
come with the global performance impact)


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