singleton_singleton_singleton.rb

class Person
  # We all know this is for putting "class methods"
  # on a class
  #
  # but this is actually a special syntax for moving into the scope
  # of a singleton class
  #
  # in this case we are moving into the scope of self's singleton's
  # class
  #
  # which in this case is Person
  class << self
  end
end

# but we don't need to always do self,
# we can access the singleton class of any object
person = Person.new

class << person
  def hello
    puts "hello from an instance of Person's singleton class!"
  end
end

person.hello

person2 = Person.new

begin
  person2.hello
rescue NoMethodError
  puts "Sorry person2 does not know about methods on Person's singleton class"
end