From: Martin DeMello <mdemello@...>
Date: 2001-12-17T10:16:10+09:00
Subject: [ruby-talk:28721] Scanning for delimited substrings

I need to scan a string for delimited substrings, and return an array (as in
String#scan) broken into the substrings and the bits between them. For
example, "one <<two>> three <<four>> five six <<seven>>" scanned for
("<<",">>") should return ["one ", "<<two>>", " three ", "<<four>>",
" five six ", "<<seven>>"]. The task is made somewhat easier by the fact
that delimiters are strictly not nested ("foo <<bar <<baz>> quux>>" should
return ["foo ", "<<bar <<baz>>", " quux"])

Anyway, I have the following (working, afaik) code; I was just wondering if
there was a better (faster and/or more elegant) way to do it. (Frinstance a
straight call to scan (and a few flattens and compacts) might do it, but I
couldn't work out the regexp).

class String
 def delimit_scan(l,r)
    a = []
    s = self.dup
    m = "(#{Regexp.quote(l)}[^\n]*?#{Regexp.quote(r)})"
    while s
      s =~ m
      if ($&)
        a << $` << $&
        s = $'
      else
        a << s
        s = nil
      end
    end
    a
  end
end

a = "the <<quick>> <<brown <<fox>> jumps over <<the>> lazy>> dog."
puts a.delimit_scan("<<",">>")

--- which returns ---
the 
<<quick>>
 
<<brown <<fox>>
 jumps over 
<<the>>
 lazy>> dog.
--------------------

Also, I left out nested delimiters because I don't need them, and I couldn't
think of a clean way to add them in without slowing things down, but if
there's a more general method that trivially handles both cases I'd like to
see it.
  
-- 
Martin DeMello