In ordinary Ruby, we could define a second method, current_user, designed to return the value of @current_user, as shown in Listing 8.21.

If we did this, we would effectively replicate the functionality of attr_accessor, which we saw in Section 4.4.5.5 The problem is that it utterly fails to solve our problem: With the code in Listing 8.21, the user’s signin status would be forgotten. As soon as the user went to another page—poof!—the session would end and the user would be automatically signed out. To avoid this problem, we can find the user corresponding to the remember token created by the code in Listing 8.19, as shown in Listing 8.22.

Listing 8.22 uses the common but initially obscure ||= (‘‘or equals’’) assignment operator (Box 8.2). Its effect is to set the @current_user instance variable to the user corresponding to the remember token, but only if @current_user is undefined.6 In other words, the construction

calls the user_from_remember_token method the first time current_user is called, but on subsequent invocations returns @current_user without hitting the database.7 This is only useful if current_user is used more than once for a single user request; in any case, find_by_remember_token will be called at least once every time a user visits a page on the site.