in reply to Regexp for range of numbers

Of course, with 5.9.2, there is a much nicer way to construct an efficient regular expression to match the numbers from 0 to 255 without leading zeroes:

use strict;
my $zero_to_255 = join "|", 0..255;
$zero_to_255 = qr(^(?:$zero_to_255)$);
print $zero_to_255,"\n";
for (-2,-1, 0..259) {
  print "$_\n" 
    unless /$zero_to_255/;
};

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Re^2: Regexp for range of numbers
by 5mi11er (Deacon) on Apr 05, 2005 at 15:52 UTC
    So, stringing together a somewhat large number of static ORs in a regular expression is efficient?
    • Programmer wise, I agree.
    • Space wise, not so much.
    • Time wise? If it is, it is counter intuitive to me...
    -Scott
[reply]

      Please note that I mentioned 5.9.2, the most current release of the developer branch, which has a patch by demerphq, that builds a very optimized tree out of a list like mine. The tree (actually a Trie) can the optimally match/compare against the string, by looking at exactly the first three chars of the string and quickly decide if it matches or not.

[reply]
        Very cool. So is there detailed information available somewhere about this new feature? I imagine it's doing some hash or binary tree type searches...

        -Scott

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