Overview

Documenting the code reading process for Ruby on Rails.

Preparation

1. Create a new project with rails new RailsCodeReading.
2. Add the following to the Gemfile:

gem 'pg'
gem 'pry-rails'
gem 'pry-doc'
gem 'pry-byebug'
gem 'byebug'

3. Run bundle config set path '.bundle' and then execute bundle install.
4. rails generate controller Example
5. Add binding.pry to railties/lib/rails/welcome_controller.rb#L9:

  def index
    binding.pry
  end

Code Reading

Let's explore how Rails invokes WelcomeController#index.

config/routes.rb does not define WelcomeController#index; Rails seems to define it by default, likely through the autoload mechanism.

railties/lib/rails.rb#L33

Autoloading it here registers WelcomeController in the routing.

Here is the implementation of WelcomeController. railties/lib/rails/welcome_controller.rb#L5

Although I couldn't follow the code in detail, Rails appears to leverage the autoload mechanism to resolve routing without explicitly registering it.