class method self.new

# File actionpack/lib/action_view/helpers/form_helper.rb, line 1234
      def initialize(object_name, object, template, options, proc)
        @nested_child_index = {}
        @object_name, @object, @template, @options, @proc = object_name, object, template, options, proc
        @parent_builder = options[:parent_builder]
        @default_options = @options ? @options.slice(:index) : {}
        if @object_name.to_s.match(/\[\]$/)
          if object ||= @template.instance_variable_get("@#{Regexp.last_match.pre_match}") and object.respond_to?(:to_param)
            @auto_index = object.to_param
          else
            raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to to_param: #{object.inspect}"
          end
        end
        @multipart = nil
      end