The next file required by +railties/lib/rails.rb+ is +application.rb+. This file defines the +Rails::Application+ constant which the application's class defined in +config/application.rb+ in a standard Rails application depends on. Before the +Rails::Application+ class is defined however, there's some other files that get required first.
The next file required by +railties/lib/rails.rb+ is +application.rb+.
This file defines the +Rails::Application+ constant which the
application's class defined in +config/application.rb+ in a standard
Rails application depends on.
The first of these is +active_support/core_ext/hash/reverse_merge+ which can be "read about in the Active Support Core Extensions guide":active_support_core_extensions.html#merging under the "Merging" section.
Before the +Rails::Application+ class is
defined however, +rails/engine+ is also loaded, which is responsible for
handling the behavior and definitions of Rails engines.
h4. +active_support/file_update_checker.rb+
TIP: You can read more about engines in the "Getting Started with Engines":engines.html
guide.
The +ActiveSupport::FileUpdateChecker+ class defined within this file is responsible for checking if a file has been updated since it was last checked. This is used for monitoring the routes file for changes during development environment runs.
h4. +railties/lib/rails/plugin.rb+
This file defines +Rails::Plugin+ which inherits from +Rails::Engine+. Unlike +Rails::Engine+ and +Rails::Railtie+ however, this class is not designed to be inherited from. Instead, this is used simply for loading plugins from within an application and an engine.
This file begins by requiring +rails/engine.rb+
h4. +railties/lib/rails/engine.rb+
The +rails/engine.rb+ file defines the +Rails::Engine+ class which inherits from +Rails::Railtie+. The +Rails::Engine+ class defines much of the functionality found within a standard application class such as the +routes+ and +config+ methods.
The "API documentation":http://api.rubyonrails.org/classes/Rails/Engine.html for +Rails::Engine+ explains the function of this class pretty well.
This file's first line requires +rails/railtie.rb+.
Among other things, Rails Engine is also responsible for loading the
