class String
  # Like #index but returns a Range.
  #
  #   require 'facet/string/range'
  #
  #   "This is a test!".rand('test')  #=> 10..13
  #
  def range(s, offset=0)
    if self.index(s, offset)
      return ($~.begin(0))..($~.end(0)-1)
    end
    nil
  end
end