Question

I can define @some_ivar outside a class. To which class does this ivar belong to and what is it’s scope?

For example,
I can say in example.rb

@var = "Hi"

and in irb, I can require example.rb and access @var

Answer 1

That var belongs to a top-level object called main.

$ irb
1.9.3p0 :001 > @var = 'Hi'
 => "Hi" 
1.9.3p0 :002 > self
 => main 
1.9.3p0 :003 > @var
 => Hi

main is basically an object with an interesting property: any method defined in its context (outside of “normal” classes) becomes available to all objects.

$ irb
1.9.3p0 :001 > def foo
1.9.3p0 :002?>   1
1.9.3p0 :003?> end
 => nil 
1.9.3p0 :004 > Object.new.foo
 => 1 
1.9.3p0 :005 > "".foo
 => 1