module AbstractController::Helpers::ClassMethods

to be made available on the view.
* method[, method] - A name or names of a method on the controller
==== Parameters

<% if logged_in? -%>Welcome, <%= current_user.name %><% end -%>
In a view:

end
end
current_user != nil
def logged_in?

end
@current_user ||= User.find_by(id: session[:user])
def current_user

helper_method :current_user, :logged_in?
class ApplicationController < ActionController::Base
to the view:
makes the +current_user+ and +logged_in?+ controller methods available
Declare a controller method as a helper. For example, the following

def helper_method(*meths)
  meths.flatten!
  self._helper_methods += meths
  meths.each do |meth|
    _helpers.class_eval <<-ruby_eval, __FILE__, __LINE__ + 1
      def #{meth}(*args, &blk)                               # def current_user(*args, &blk)
        controller.send(%(#{meth}), *args, &blk)             #   controller.send(:current_user, *args, &blk)
      end                                                    # end
    ruby_eval
  end
end