guess

# File lib/optparse.rb, line 485
    def self.guess(arg)
      case arg
      when ""
        t = self
      when /\A=?\[/
        t = Switch::OptionalArgument
      when /\A\s+\[/
        t = Switch::PlacedArgument
      else
        t = Switch::RequiredArgument
      end
      self >= t or incompatible_argument_styles(arg, t)
      t
    end