From: "Weirich, James" <James.Weirich@...>
Date: 2003-11-20T00:49:09+09:00
Subject: Re: $& write-protected?

From: matz@ruby-lang.org [mailto:matz@ruby-lang.org]
> If you update $~ (the match result), $&, $1, etc. would follow
> accordingly.  So that the better RCR should be to create MatchData
> without built-in regular expression match, I think.

Wow, this solves a problem I was dealing with.  I wanted to implement "sub"
on a array-like object such that list.sub(...) would be the same a calling
sub on each element of the list.  The problem was that list.sub(/re/) { $1 }
would always give nil for the value of $1.

Here's my solution.

# -----------------------------------------------
class FileList < Array
  class << self
    attr_accessor :match_data
    def set_match_data(md, block)
      FileList.match_data = md
      eval "$~ = FileList.match_data", block
    end
  end
  def sub(re, &block)
    collect do |item|
      item.sub(re) {
        FileList.set_match_data($~, block)
        block.call
      }
    end
  end
end

f = FileList.new
f << "a.c" << "b.c"
p f.sub(/^(.*)\.c$/) { "#{$1}.o" }
# ---------------------------------------------

The above solution is not thread safe, but that can be easily solved by
using a mutex in set_match_data.  Comments welcome.

-- 
-- Jim Weirich / Compuware
-- FWP Capture Services
-- Phone: 859-386-8855