# Self.some\_attribute vs @some\_attribute

**URL:** <https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687>\
**Category:** Ruby\
**Created:** [April 2, 2006, 10:40pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687 "2006-04-02T22:40:50Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 2, 2006, 10:40pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/1 "2006-04-02T22:40:50Z")

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Hello,

I just finished reading the Agile book. Of course I forgot at least the  
two thirds of what I read. I started reading the source code of Typo, to  
see a real (and Rails) application.

I stumbled upon this snippet of code:

def crypt\_unless\_empty  
if password(true).empty?  
user = self.class.find(self.id)  
self.password = user.password  
else  
write\_attribute “password”, self.class.sha1(password(true))  
@password = nil  
end  
end

is there any practical reason to use sometimes self.password and  
sometimes @password? I thought they were synonyms…

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**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 2, 2006, 11:21pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/2 "2006-04-02T23:21:54Z")

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Fred wrote:

> ```
> user = self.class.find(self.id)
> self.password = user.password
> else
> write_attribute "password", self.class.sha1(password(true))
> @password = nil
> end
> 
> ```
> 
> end
> 
> is there any practical reason to use sometimes self.password and  
> sometimes @password? I thought they were synonyms…

The difference between `self.attr = val' and`@attr = val’ is simply  
that the first is a method call, i.e. the same as `self.attr=(val)'. The`attr=’ method may check the value, and do a lot of different things -  
when you use `@attr = val', the only thing happening is that you assign the instance variable`attr’ the value of `val’. Take this, for  
instance:

class User  
attr\_reader :name

```
 def initialize(name)
   # @name will be a string
   self.name = name
 end

 def name=(val)
   # make sure @name is a string
   @name = val.to_str
 end

```

end

Cheers,  
Daniel

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<div class="post-metadata">

**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 3, 2006, 12:13am UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/3 "2006-04-03T00:13:47Z")

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Fred wrote:

> is there any practical reason to use sometimes self.password and  
> sometimes @password? I thought they were synonyms…

@password refers to an instance variable.

self.password refers to a method named ‘password’, which may or may not  
have anything to do with any instance variables.

People will often use methods to get and set instance variable values to  
allow for code that checks values, handles business logic, and so on.

But methods and instance variables are not coupled, and one shouldn’t  
assume that any given method is interacting with an instance variable of  
the same name.

–  
James B.

[http://web2.0validator.com](http://web2.0validator.com) - We’re the Dot in Web 2.0  
[http://refreshingcities.org](http://refreshingcities.org) - Design, technology, usability  
[http://yourelevatorpitch.com](http://yourelevatorpitch.com) - Finding Business Focus  
[http://www.jamesbritt.com](http://www.jamesbritt.com) - Playing with Better Toys

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<div class="post-metadata">

**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 3, 2006, 2:31pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/4 "2006-04-03T14:31:24Z")

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Fred wrote:

> is there any practical reason to use sometimes self.password and  
> sometimes @password? I thought they were synonyms…

self.password = … # calls the method “password=”

It’s a method call. You might assume from the name it sets @password,  
but it may do other stuff as well (e.g. checks, or in this case, encrypt  
the given password string).

In an ActiveRecord subclass (as this appears to be) password=(foo) is a  
method that just calls write\_attribute(“password”, foo), simply setting  
the password attribute of the active record. There’s no @password  
involved, only @attributes[“password”].

Of course, this method can be overridden, and it probably is in the  
class you’re looking at. Look for the line beginning “def password=” for  
more clues.

Cheers,  
Dave

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<div class="post-metadata">

**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 3, 2006, 2:38pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/5 "2006-04-03T14:38:08Z")

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On 4/2/06, Fred [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ```
> user = self.class.find(self.id)
> self.password = user.password
> else
> write_attribute "password", self.class.sha1(password(true))
> @password = nil
> end
> 
> ```
> 
> end
> 
> is there any practical reason to use sometimes self.password and  
> sometimes @password? I thought they were synonyms…

Rails is a bit different in this scenario than most other Ruby programs.  
The attributes in your model classes that are picked up at runtime  
from your database schema are not defined as regular methods.  
@blah = ‘something’ will not necessarily do what you expect to the  
value in the ‘blah’ column of your table.  
If you’re using an accessor you defined yourself, self.something and  
@something are equivalent. If you’re using an ActiveRecord attribute,  
you should exclusively use self.something or self[:something].

–Wilson.

---

<div class="post-metadata">

**Author:** ![fred](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/db5fbb/32.png) [@fred](https://www.ruby-forum.com/u/fred)\
**Post date:** [April 3, 2006, 7:25pm UTC](https://www.ruby-forum.com/t/self-some-attribute-vs-some-attribute/56687/6 "2006-04-03T19:25:49Z")

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> Rails is a bit different in this scenario than most other Ruby programs.  
> The attributes in your model classes that are picked up at runtime  
> from your database schema are not defined as regular methods.  
> @blah = ‘something’ will not necessarily do what you expect to the  
> value in the ‘blah’ column of your table.  
> Indeed, I just noticed this.

In that case, it appears the instance variable is used to do some  
manipulations I still need to understand before writing the crypted  
value to the database.

Thanks