```ruby
require 'generators/slim/controller/controller_generator'

module Slim
  module Generators
    class MailerGenerator < ControllerGenerator
      source_root File.expand_path(File.join('..', 'templates'), __FILE__)

      def copy_view_files
        if ::Rails.version.to_s >= "4.2.0"
          view_base_path = File.join("app/views", class_path, file_name)
          empty_directory view_base_path

          if self.behavior == :invoke
            formats.each do |format|
              layout_path = File.join("app/views/layouts", filename_with_extensions("mailer", format))
              template filename_with_extensions(:layout, format), layout_path
            end
          end

          actions.each do |action|
            @action = action

            formats.each do |format|
              @path = File.join(view_base_path, filename_with_extensions(action, format))
              template filename_with_extensions(:view, format), @path
            end
          end
        else
          super
        end
      end

      protected
      def format
        :text
      end

      def formats
        [:text, :html]
      end

    end
  end
end
```

Switch inheritance for Slim's `MailerGenerator`
user
```ruby
require 'rails/generators/erb/mailer/mailer_generator'

module Slim
  module Generators
    class MailerGenerator < Erb::Generators::MailerGenerator
      source_root File.expand_path(File.join('..', 'templates'), __FILE__)

      protected
      def format
        :text
      end

      def formats
        [:text, :html]
      end

      def handler
        :slim
      end
    end
  end
end
```
assistant