Override current_user in ApplicationController throws undefined method error

问题

Based on stackoverflow question for overriding current_user of devise, I wrote something like this:

class ApplicationController < ActionController::Base
    alias_method :devise_current_user, :current_user
    def current_user
        if !devise_current_user.nil?
            return # my logic
        end
        return nil
    end
end

Two questions: 1. It throws an undefined method error where I define alias_method .... 2. In the devise_for method, will my overriden current_user will be passed or the devise's current_user?

来源：https://stackoverflow.com/questions/12465324/override-current-user-in-applicationcontroller-throws-undefined-method-error