Question

I am having a terrible time understanding the assignment function that is needed, as explained in chapter 8.2.3. of the Hartl’s tutorial.

As context, he is focused on the second line of the following sign_in function:

  def sign_in(user)
    cookies.permanent[:remember_token] = user.remember_token
    self.current_user = user #<-- this line
  end

Where he mentions because its an assignment, it must be then separately defined as

def current_user=(user)
    @current_user = user
end

Where the method current_user= expressly designed to handle assignment to current_user. My confusions is:

1. Why is this even necessary? I thought that a simple = would allow you to assign things. For example user.email = [e-mail]

2. Also, when eventually he will code redirect_to current_user, how does something that belongs to the SessionsController get translated to a view controlled by UsersController?

Thanks!!

Answer 1

The reason being it is needed as to avoid confusion (for the interpreter/VM) between method invocation and variable assignment

def foo
  # Two completely different things!
  bar = "baz" # assigns baz to local variable bar
  self.bar = "baz" # invokes the bar= method with parameter of baz
end

What’s happening there is that he is doing two things, firstly invoking the current_user= method with the user object and secondly, setting that to @current_user (it’s not a great example – you’d probably end up doing a lot more in real life if you were to make a current_user= method such as setting up session variables).

secondly redirect_to current_user is equivalent to redirect_to user_path(current_user) – check out http://api.rubyonrails.org/classes/ActionController/Redirecting.html for more details which explains the different parameter kinds that redirect_to can take. Note this is a redirect, not a render – so a second HTTP request happens here.