From: "Maurício" <briqueabraque@...>
Date: 2002-08-07T09:11:56+09:00
Subject: Very ineficient regular expression match

Hi,

    The following code is supposed to print multiple regular expression
matches on a given string:

class Myregexp < Regexp
 def each (str)
  pos = 0
  while ((pos<str.size) && (m = match(str[pos...str.size])))
   yield m
   pos += m.end(0)
  end
 end
end

Myregexp.new(/pattern/).each("string"){|m| $stdout << m[0]}

    It works. However, it takes a lot of time and memory when "string" is
big. In my case, with a 10Mb string, it takes 40Mb of RAM. The problem comes
from the str[pos...str.size] (I solved the problem for my situation with a
hack where I changed it for str[pos,300], and everything runs fast and with
low memory). Since Ruby uses garbage collection and strings are, I believe,
copy on write, why does this occur?
    I'm using Pragmatic Programmers Ruby 1.66 with Windows XP.

    Thanks,
    Maur�cio