require 'abstract_controller'
require 'action_mailer/version'
# Common Active Support usage in Action Mailer
require 'active_support/rails'
require 'active_support/core_ext/class'
require 'active_support/core_ext/module/attr_internal'
require 'active_support/core_ext/string/inflections'
require 'active_support/lazy_load_hooks'
module ActionMailer
extend ::ActiveSupport::Autoload
eager_autoload do
autoload :Collector
end
autoload :Base
autoload :DeliveryMethods
autoload :InlinePreviewInterceptor
autoload :MailHelper
autoload :Preview
autoload :Previews, 'action_mailer/preview'
autoload :TestCase
autoload :TestHelper
autoload :MessageDelivery
autoload :DeliveryJob
end
autoload :Mime, 'action_dispatch/http/mime_type'
ActiveSupport.on_load(:action_view) do
ActionView::Base.default_formats ||= Mime::SET.symbols
ActionView::Template::Types.delegate_to Mime
end任务是阅读一些开源项目里真实的代码，完全看不懂额。