Pure Ruby StringScanner

strscan.rb

class StringScanner
  attr_reader :string

  def initialize(string, *args)
    @string = string
    @pos = 0
    @last_match = nil
  end

  def scan(re)
    if @string.byteindex(/\G#{re}/, @pos)
      @pos = $~.byteoffset(0)[1]
    end
    @last_match = $~
    $&
  end

  def method_missing(mid, ...)
    @last_match.send(mid, ...)
  end
end