new

# File actionview/lib/action_view/helpers/form_helper.rb, line 1715
      def initialize(object_name, object, template, options)
        @nested_child_index = {}
        @object_name, @object, @template, @options = object_name, object, template, options
        @default_options = @options ? @options.slice(:index, :namespace, :skip_default_ids, :allow_method_names_outside_object) : {}
        @default_html_options = @default_options.except(:skip_default_ids, :allow_method_names_outside_object)

        convert_to_legacy_options(@options)

        if @object_name&.end_with?("[]")
          if (object ||= @template.instance_variable_get("@#{@object_name[0..-3]}")) && 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
        @index = options[:index] || options[:child_index]
      end