def cleanup(x)
  s = x.read
  return s.gsub(/BAD_CHARS/, '')
end


s = "my string with bad cars"

cleanup(s) # Exception, no method error 'read' for class String

# ok, let's ducktype s
class String
  def read
    return self
  end
end

cleanup(s) # whoot works.

# if it walks like a duck and talks like a duck, then it must be....