Ruby creating instance variables outside a class

Question

What does it mean to create an instance variable, say @foo in a file outside any class definition. Say there is a file, test.rb and the entire contents of the file are given below.

# test.rb
@foo = "bar"
puts @foo

It prints "bar", but is this an instance variable in some sort of wrapping class?

Testing using two files indicates that there is a main object that everything is wrapped inside. Is this understanding correct?

Contents of a.rb

@me = self
@a = "from-a"

Contents of b.rb

require "./a"

@b = "from-b"
puts @me == self # true (self refers to the same object)
puts self.class  # Object
puts self.instance_variables # [@a, @b, @me]

Mike Lewis · Accepted Answer · 2011-04-16 16:16:28Z

18

Everything is an object in ruby. So you are actually in the main object right now, which is an instance of Object.

In your file, if you put puts self.class, you will see you are operating under main, and the class being Object.

Even in irb, for example:

ruby-1.9.2-p136 :001 > self
 => main 
ruby-1.9.2-p136 :002 > self.class
 => Object

edited Apr 16, 2011 at 16:16

answered Apr 16, 2011 at 2:24

Mike Lewis

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2 Comments

Anurag Over a year ago

Is main an instance of Object that everything operates under?

johnsimer Over a year ago

how is the main Object shared in a multi-user web application? e.g. let's say I have a file 'x.rb' I import in a Rails or Sinatra application. If one user requests calls a method in that file that sets @a = 5, and then another user calls a method in that file that retrieves @a, will the second user receive a value of 5? Or Do Rails/Sinatra create a separate instance of the Object class of that file for each separate user request?

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