# Learning ruby question

**URL:** <https://www.ruby-forum.com/t/learning-ruby-question/93142>\
**Category:** Rails\
**Created:** [April 28, 2007, 5:52am UTC](https://www.ruby-forum.com/t/learning-ruby-question/93142 "2007-04-28T05:52:44Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![jim](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ac91a4/32.png) [@jim](https://www.ruby-forum.com/u/jim)\
**Post date:** [April 28, 2007, 5:52am UTC](https://www.ruby-forum.com/t/learning-ruby-question/93142/1 "2007-04-28T05:52:44Z")

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I’m having trouble understanding Ruby’s concept of scope. Could  
someone explain the difference between the following 2 programs.  
They both return the same output “aaaaaaaa”, but I’m just not sure  
about self in #1. Is self.day and self.title referring to and setting  
class variables or are they instance variables? Thanks in advance.

# 1.

class Session  
attr\_accessor :day, :title

def initialize()  
self.day = “aaaaaaaa”  
self.title = “bbbbb”  
end  
end

s=Session.new  
puts s.day  
###################

# 2.

class Session  
attr\_accessor :day, :title

def initialize()  
@day = “aaaaaaaa”  
@title = “bbbbb”  
end  
end

s=Session.new  
puts s.day  
###################

---

<div class="post-metadata">

**Author:** ![jim](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ac91a4/32.png) [@jim](https://www.ruby-forum.com/u/jim)\
**Post date:** [April 28, 2007, 7:17am UTC](https://www.ruby-forum.com/t/learning-ruby-question/93142/2 "2007-04-28T07:17:47Z")

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In both cases you’re setting instance variables. Class variables are  
designated with ‘@@’, and instance variables are usually designated  
with ‘@’. But as you’ve seen, you can also set instance variables up  
using the ‘self’ reference, which is just a reference to the object  
receiving the message. Without the ‘self’ in #1, day and title would  
wind up being local variables that would fall out of scope as soon as  
initialize() ended.

If you’re familiar with Java, you can think of ‘self’ as ‘this’.

As a thought experiment, what do you think the following code will do?

class Session  
attr\_accessor :day, :title  
def initialize()  
self.day = ‘aaa’  
self.title = ‘bbb’  
end  
def say\_day  
puts @day # Accessing day like any other instance variable, with  
‘@’. Think it’ll work?  
end  
end  
s = Session.new  
s.say\_day

---

<div class="post-metadata">

**Author:** ![jim](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ac91a4/32.png) [@jim](https://www.ruby-forum.com/u/jim)\
**Post date:** [April 29, 2007, 4:27am UTC](https://www.ruby-forum.com/t/learning-ruby-question/93142/3 "2007-04-29T04:27:10Z")

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Great thanks. So in my 2 examples above - the code is functionally  
the same. You can SET instance variables within a class using either  
@var = foo OR self.var = foo

As for your example, based on what I’ve said above - it appears you  
can also GET instance variables using self.var or @var - so the output  
should be: aaa

Is that correct?

Thanks again.

---

<div class="post-metadata">

**Author:** ![jim](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ac91a4/32.png) [@jim](https://www.ruby-forum.com/u/jim)\
**Post date:** [April 29, 2007, 5:01am UTC](https://www.ruby-forum.com/t/learning-ruby-question/93142/4 "2007-04-29T05:01:11Z")

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On 4/28/07, jim [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Great thanks. So in my 2 examples above - the code is functionally  
> the same. You can SET instance variables within a class using either  
> @var = foo OR self.var = foo
> 
> As for your example, based on what I’ve said above - it appears you  
> can also GET instance variables using self.var or @var - so the output  
> should be: aaa
> 
> Is that correct?

That is correct. But don’t take my word for it - run it and see what it  
does. 🙂

The best way to learn how all this stuff works is to play with it. If  
you think something might work a certain way, try it and see. If it  
doesn’t do what you expected, find out why. Interactive Ruby (irb) is  
your friend.

–  
Bill K.