class Thor::Options

def check_unknown!
  to_check = @stopped_parsing_after_extra_index ? @extra[0...@stopped_parsing_after_extra_index] : @extra
  # an unknown option starts with - or -- and has no more --'s afterward.
  unknown = to_check.select { |str| str =~ /^--?(?:(?!--).)*$/ }
  raise UnknownArgumentError.new(@switches.keys, unknown) unless unknown.empty?
end