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Re^3: Compiling Regular Expressions

by hv (Parson)
on Feb 19, 2003 at 14:21 UTC ( #236634=note: print w/ replies, xml ) Need Help??

in reply to Re^2: Compiling Regular Expressions
in thread Compiling Regular Expressions

/o can still be useful from time to time. Firstly, you occasionally expect that the interpolated variable may change but still want to use the original value (but this is rare). Secondly, the "recompile only if changed" logic requires checking whether the pattern has changed, which takes time:

perl -MBenchmark -w ($s, $t) = qw/ foo xfoox /; timethese(-1, { oful => q{ $t =~ /$s/o }, oless => q{ $t =~ /$s/ }, }) __END__ Benchmark: running oful, oless for at least 1 CPU seconds... oful: 2 wallclock secs ( 1.08 usr + 0.00 sys = 1.08 CPU) @ +2427258.33/s (n=2621439) oless: 2 wallclock secs ( 1.15 usr + 0.00 sys = 1.15 CPU) @ +1841144.35/s (n=2117316)


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Re^4: Compiling Regular Expressions
by diotalevi (Canon) on Feb 19, 2003 at 14:35 UTC

    And I was expecting that the programmer who knows the expression should use the original value is better off just using qr instead of /o. The difference is in binding the regex permanently to the optree and at least having the option to alter things with qr.

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