From: Robert Klemme <bob.news@...>
Date: 2004-01-21T02:20:04+09:00
Subject: Re: regex help

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"Nikolai Weibull" <ruby-talk@pcppopper.org> schrieb im Newsbeitrag
news:20040120165640.GB1987@puritan.bredbandsbolaget.se...
> * Robert Klemme <bob.news@gmx.net> [Jan, 20 2004 17:30]:
> > > str.gsub!(/"[^"\\]*(\\.[^"\\]*)*"|\*\//){ |m| m == '\*' ? '*\\' :
m }
> > Did you test that?  I'm afraid, it doesn't work:
> yes, but i seem to have made a mistake in copying it over for some
> reason, the problem is the test, not the regex, it should be
>
> str.gsub!(/"[^"\\]*(\\.[^"\\]*)*"|\*\//){ |m| m == '*/' ? '*\\' : m }
>     ^^

Oops, yes you're right.

> > If you want to allow quotes to be escaped, this one is the way to go:
> >
> > irb(main):012:0> puts str.gsub(%r{"([^"\\]|\\")*"|\*/}) {|m| m == '*/'
?
> > '*\\' : m}
> >   /* comment *\  String s = "***/";
> well, this isn't really correct, that would only escape quotes and you
> wouldn't allow for escaped backslashes in your strings....it is of
> course trivial to mend.  do note that my version is a lot faster...see
> "Mastering Regular Expressions" by Jeffrey E. F. Friedl on why this is
> so.  anyway, thanks for pointing out that something was wrong,
> nikolai

I've added escaping of arbitrary chars and put it into a benchmark
(attached).  The differences don't look too big:

18:07:21 [ruby]: ./rx-bm.rb
      user     system      total        real
mine  1.781000   0.000000   1.781000 (  1.776000)
yours  1.719000   0.000000   1.719000 (  1.732000)
18:07:26 [ruby]: ./rx-bm.rb
      user     system      total        real
mine  1.781000   0.000000   1.781000 (  1.785000)
yours  1.704000   0.000000   1.704000 (  1.712000)
18:07:31 [ruby]: ./rx-bm.rb
      user     system      total        real
mine  1.781000   0.000000   1.781000 (  1.800000)
yours  1.719000   0.000000   1.719000 (  1.706000)
18:07:36 [ruby]: ./rx-bm.rb
      user     system      total        real
mine  1.781000   0.000000   1.781000 (  1.788000)
yours  1.703000   0.000000   1.703000 (  1.693000)
18:07:43 [ruby]: ./rx-bm.rb
      user     system      total        real
mine  1.766000   0.000000   1.766000 (  1.788000)
yours  1.719000   0.000000   1.719000 (  1.707000)
18:07:52 [ruby]:

That's certainly not what I'd call "a lot faster".  Maybe the effects of
GC dominate the rx timing.  Here's the output of the second benchmark:

18:15:22 [ruby]: ./rx-bm-2.rb
      user     system      total        real
mine  3.234000   0.000000   3.234000 (  3.227000)
yours  3.157000   0.016000   3.173000 (  3.188000)
18:15:33 [ruby]: ./rx-bm-2.rb
      user     system      total        real
mine  3.203000   0.000000   3.203000 (  3.218000)
yours  3.125000   0.016000   3.141000 (  3.231000)
18:15:44 [ruby]: ./rx-bm-2.rb
      user     system      total        real
mine  3.187000   0.000000   3.187000 (  3.257000)
yours  3.156000   0.000000   3.156000 (  3.186000)

Doesn't look so much different.  Any ideas or enlightening comments from
the aforementioned book?

Kind regards

    robert

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#!/usr/bin/ruby

require 'benchmark'
include Benchmark

N=3D100000

str =3D '  /* comment */  String s =3D "***/";  '

bm do |x|
  x.report("mine") do
    for n in 1..N
      str.gsub(%r{"([^"\\]|\\.)*"|\*/}) {|m| m =3D=3D '*/' ? '*\\' : m}
    end
  end

  x.report("yours") do
    for n in 1..N
      str.gsub(/"[^"\\]*(\\.[^"\\]*)*"|\*\//){ |m| m =3D=3D '*/' ? '*\\' =
: m }
    end
  end
end

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#!/usr/bin/ruby

require 'benchmark'
include Benchmark

N=3D100000

str =3D '  /* comment */  String s =3D "***/";  '

a_mine =3D (1..N).map{str.dup}
a_yours =3D (1..N).map{str.dup}

bm do |x|
  x.report("mine") do
    a_mine.each do |str|
      str.gsub!(%r{"([^"\\]|\\.)*"|\*/}) {|m| m =3D=3D '*/' ? '*\\' : m}
    end
  end

  x.report("yours") do
    a_yours.each do |str|
      str.gsub!(/"[^"\\]*(\\.[^"\\]*)*"|\*\//){ |m| m =3D=3D '*/' ? =
'*\\' : m }
    end
  end
end

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