Why is foo returning nil in last line?

ruby_scope_problem.rb

$ irb
ruby-1.9.3-p0 :001 > def foo
ruby-1.9.3-p0 :002?>   1
ruby-1.9.3-p0 :003?> end
 => nil 
ruby-1.9.3-p0 :004 > foo
 => 1 
ruby-1.9.3-p0 :005 > if false
ruby-1.9.3-p0 :006?>   foo = 2
ruby-1.9.3-p0 :007?> end
 => nil 
ruby-1.9.3-p0 :008 > foo
 => nil 

I would say because of foo is not set (if false). Object.foo returns 1

@dreewill but Object.foo works only in irb

@unnu def foo and foo are in this same scope.

Simply

if false
  foo = 2
end

is equivalent to

foo = 2

since in first case foo is not set, but is visible to interpreter, so is set to nil

But it's not true for instance variables for example.