From: Roman Hausner <roman.hausner@...>
Date: 2006-07-28T01:41:05+09:00
Subject: Slow regular expressions :(

I am disappointed to learn that Ruby obviously implements yet another 
regular expression library that does not avoid very slow matching 
failures.

Just try this program:

str1 = "foo " * 70 + "foo ";
str2 = "foo " * 70 + "fo ";

strings = str1, str2;

strings.each { |s|
  print "Matching #{s}\n";
  if(s =~ /^(\s*foo\s*)*$/)
    print "YES!\n";
  else
    print "NO!\n";
  end
}

and compare it with this perl program:
my $str1 = ("foo " x 70) . "foo ";
my $str2 = ("foo " x 70) . "fo ";

my @strings = ( $str1, $str2 );

foreach $s ( @strings ) {
print "Matching $s\n";
if($s =~ /^(\s*foo\s*)*$/) {
  print "YES!\n";
} else {
  print "NO!\n";
}
}

On my machine, the perl version takes 0.229 seconds. The ruby version 
was still running after 519.662 seconds when I killed it.

Is this being taken care of for the next release?

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