# Self. vs. @

**URL:** <https://www.ruby-forum.com/t/self-vs/111950>\
**Category:** Rails\
**Created:** [August 13, 2007, 8:11pm UTC](https://www.ruby-forum.com/t/self-vs/111950 "2007-08-13T20:11:45Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 8:11pm UTC](https://www.ruby-forum.com/t/self-vs/111950/1 "2007-08-13T20:11:45Z")

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I’m working on an application that creates a confirmation e.mail  
whenever you create and account or change an e.mail address. I  
thought I’d just use the same key generation code used for the  
password hash login example from the Agile Rails book.

The function to create a salt value keeps failing complaining I have a  
nil object where I don’t expect it.

The code where it breaks is:

def create\_new\_salt  
self.salt = @user\_id.to\_s + rand.to\_s  
end

I’ve also put a constant string assigned to self.salt, but the error  
still occurs, as if self.salt points to a nil object, but I don’t see  
how that can happen. I also don’t understand any reason for this  
function to call self.salt, instead of @salt. Any clues would be much  
appreciated.

Thanks,  
j

PS here is the table definition for this model.

:created\_at, :timestamp  
:email, :string  
:type, :string #which of several e.mail columns in ‘user’ does this  
change apply to  
:user\_id, integer  
:key, :string #randomly generated key  
:salt, :string

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 8:56pm UTC](https://www.ruby-forum.com/t/self-vs/111950/2 "2007-08-13T20:56:50Z")

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That code seems to be fine. Look at where create\_new\_salt is being  
called, it’s probably being called on a nil Object instead of an AR  
model, possible a find condition returning nil instead of the  
model(s).

Vish

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 9:14pm UTC](https://www.ruby-forum.com/t/self-vs/111950/3 "2007-08-13T21:14:51Z")

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Thanks for your help. create\_new\_salt is only ever called from within  
the the model object. Here is the only function that calls it:

def initialize(id, address, type)  
@email = address  
@type = type  
@user\_id = id  
create\_new\_salt  
self.key = self.encrypt\_key(self.email, self.salt)  
end

Perhaps I can’t call it until after initialize has run? Also I still  
don’t understand why I should call self.salt in some of these cases  
and not @salt.

Thanks,  
j

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 9:32pm UTC](https://www.ruby-forum.com/t/self-vs/111950/4 "2007-08-13T21:32:55Z")

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Thanks for the info. I do realize that one is a function and the  
other is the member.

What I’m still unclear on is why in an ActiveRecord derived object one  
would choose to use one over the other. If there is logic happening  
with the self.name assignment, then why would we not always call  
self.name in ActiveRecord objects as a rule, however that doesn’t seem  
to be the case. In the book examples several members were assigned as  
@some\_data = something, while this salt value was set with  
self.salt.

Thanks,  
j

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 9:25pm UTC](https://www.ruby-forum.com/t/self-vs/111950/5 "2007-08-13T21:25:53Z")

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Joshua K. wrote:

> how that can happen. I also don’t understand any reason for this  
> function to call self.salt, instead of @salt. Any clues would be  
> much  
> appreciated.

I don’t know much about the book example you refer to but you seem to  
have some confusion between “self.salt = foo” and “@salt = foo”

When you do “@salt = foo” it is simply making the instance variable  
“salt” point to whatever “foo” is pointing at. If you do “self.salt =  
foo” then you are calling the method “salt=” with the argument “foo”.  
The method “salt=” could do anything. One might think it is typically  
defined as:

def salt=(val)  
@salt = val  
end

but it could be defined as

def salt=(val)  
@salt = rand  
end

Sounds like you need to see how “salt=” is defined. Until then you won’t  
know why it is not working.

Eric

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 9:40pm UTC](https://www.ruby-forum.com/t/self-vs/111950/6 "2007-08-13T21:40:56Z")

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Well, there you have it, you can’t easily override initialize for AR  
objects. It shouldn’t work alright with create\_new\_salt being removed  
from there too.

See this:  
[http://blog.hasmanythrough.com/2007/1/22/using-faux-accessors-to-initialize-values](http://blog.hasmanythrough.com/2007/1/22/using-faux-accessors-to-initialize-values)

What you’re trying to do can possibly be done like this:

Model.new(:email =\> address, :type =\> type, :user = user) and an  
after\_initialize callback.

Also, usually, @salt = and self.salt = are the same thing inside a  
model. salt= is a function equivalent to this:

def salt=(var)  
@salt = var  
end

(it’s part of an attr\_accessor definition.) If you didn’t have the  
accessor tho, you wouldn’t be able to call it from outside the model  
since instance variables are private.

Vish

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 10:52pm UTC](https://www.ruby-forum.com/t/self-vs/111950/7 "2007-08-13T22:52:08Z")

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Joshua K. wrote:

> What I’m still unclear on is why in an ActiveRecord derived object one  
> would choose to use one over the other. If there is logic happening  
> with the self.name assignment, then why would we not always call  
> self.name in ActiveRecord objects as a rule, however that doesn’t seem  
> to be the case. In the book examples several members were assigned as  
> @some\_data = something, while this salt value was set with  
> self.salt.

I in general always use the function version. That way if there is  
custom logic it will run. If there is not then it will work just like  
assigning a instance variable. I guess to me the function encapsulates  
better.

Eric

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<div class="post-metadata">

**Author:** ![jkahn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/53a042/32.png) [@jkahn](https://www.ruby-forum.com/u/jkahn)\
**Post date:** [August 13, 2007, 9:58pm UTC](https://www.ruby-forum.com/t/self-vs/111950/8 "2007-08-13T21:58:02Z")

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On Aug 13, 12:40 pm, “Vishnu G.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Well, there you have it, you can’t easily override initialize for AR  
> objects. It shouldn’t work alright with create\_new\_salt being removed  
> from there too.
> 
> See this:[http://blog.hasmanythrough.com/2007/1/22/using-faux-accessors-to-init](http://blog.hasmanythrough.com/2007/1/22/using-faux-accessors-to-init)…

Great thanks, that’s my issue. I’m still not clear on why various  
examples (including the book) switch between @member, and self.member,  
but just changing this to a different function then initialize has  
gotten me past the nil error.

Thanks!  
j