memoization in rails using an instance variable

Question

I'm following railstutorial by Michael Hartl. In chapter 8.2.2 he defines a variable @current_user and a method current_user.

app/helpers/sessions_helper.rb looks like this:

module SessionsHelper

  # Logs in the given user.
  def log_in(user)
    session[:user_id] = user.id
  end

  # Returns the current logged-in user (if any).
  def current_user
    @current_user ||= User.find_by(id: session[:user_id])
  end

end

Hartl defines @current_user an instance variable (of User object I guess); How can @current_user be an instance variable if it is itself an instance of the User class?

Answer 1

The SessionsHelper module is mixed into your controllers, so @current_user will be set as an instance variable of the controller which is handling the current request (Rails creates a new controller instance to handle each request)