# File lib/getoptlong.rb, line 244
  def ordering=(ordering)
    #
    # The method is failed if option processing has already started.
    #
    if @status != STATUS_YET
      set_error(ArgumentError, "argument error")
      raise RuntimeError,
        "invoke ordering=, but option processing has already started"
    end

    #
    # Check ordering.
    #
    if !ORDERINGS.include?(ordering)
      raise ArgumentError, "invalid ordering `#{ordering}'"
    end
    if ordering == PERMUTE && ENV.include?('POSIXLY_CORRECT')
      @ordering = REQUIRE_ORDER
    else
      @ordering = ordering
    end
  end