Q:

Rails -- self vs. @

I am following Michael Hartl's RoR tutorial, and it is covering the basics of password encryption. This is the User model as it currently stands:
class User < ActiveRecord::Base
    attr_accessor :password

    attr_accessible :name, :email,: password, :password_confirmation

    email_regex = /^[A-Za-z0-9._+-]+@[A-Za-z0-9._-]+\.[A-Za-z0-9._-]+[A-Za-z]$/
                                              #tests for valid email addresses.

    validates :name, :presence => true,
                     :length => {:maximum => 50}
    validates :email, :presence => true,
                      :format => {:with => email_regex},
                      :uniqueness => {:case_sensitive => false}
    validates :password, :presence => true,
                         :length => {:maximum => 20, :minimum => 6},
                         :confirmation => true

    before_save :encrypt_password

    private

    def encrypt_password
        self.encrypted_password = encrypt(password)
    end

    def encrypt(string)
        string
    end
end

I posted a previous question about before_save not working, and it turns out that what I had accidentally done is written my encrypt_password as:
def encrypt_password
    @encrypted_password = encrypt(password)
end

I understand that if self.encrypted_password sets the encrypted_password attribute, but why does @encrypted_password not do that as well?  In the response to the previous post about before_save not working someone said that the instance variable was "forgotten" after the method ended with the way I had originally coded it -- why was this the case?  Can someone please explain how self and @ work differently in the context of the code above?
NOTE: I already took a look at the posts here and here, but they both say that "self" is calling the attribute = method, and I don't even understand how that method could exist here since I never created it or declared the encrypted_password w/ attr_accessor.  So I am still confused, and this is not a re-posting of those questions.

A:

The accessors for encrypted_password have been automatically added by Rails for you because a field by that name exists in the users table.
Any field you add to a table will be automatically made available via self.field_name.
Here is where Michael Hartl's tutorial creates the encrypted_password field in the users table.
Also look at the user_spec.rb (Listing 7.3) in the linked page, where the author is testing for the presence of the encrypted_password field.
UPDATED:
As @mu points out, the @ is used for Ruby instance variables (aka "iv"). But encrypted_password is an "attribute" defined by Rails, and is not an instance variable. 
If you run User.find(1).instance_variables, you will see that there is an iv called @attributes, which is of type Hash.
Inside that iv is where the encrypted_password is stored. Rails has defined accessor methods for encrypted_password, which gets/sets the data for that
attribute in the @attributes Hash. 
Note that you could also get/set the data via @attributes["encrypted_password"] called from within the User class (but the accessor methods are convenient way to do just that).

