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comp.lang.ruby

self.some_attribute vs @some_attribute

Fred

4/2/2006 8:41:00 PM

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...

--
Posted via http://www.ruby-....
5 Answers

Daniel Schierbeck

4/2/2006 9:16:00 PM

0

Fred wrote:
> 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...

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

james_b

4/2/2006 10:13:00 PM

0

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 Britt

http://web2.0val... - We're the Dot in Web 2.0
http://refreshing... - Design, technology, usability
http://yourelevato... - Finding Business Focus
http://www.jame... - Playing with Better Toys

Dave Burt

4/3/2006 12:26:00 PM

0

Fred wrote:
> 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...

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

Wilson Bilkovich

4/3/2006 12:34:00 PM

0

On 4/2/06, Fred <0bssel602@sneakemail.com> wrote:
> 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...
>

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.

Fred

4/3/2006 5:26:00 PM

0


> 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

--
Posted via http://www.ruby-....