class Foo
  # Write the instance variable foo into the class Foo
  @@foo = 14

  x = Foo.new

  def x.foo
    # Reads the instance variable foo from the class of Self, which is Foo
    puts @@foo
  end

  x.foo

  def self.foo
    # Reads the instance variable foo from self
    puts @@foo
  end

  self.foo
end

puts Foo.foo