Singleton Class

singleton_class.rb

puts <<-EOL

1. finding method

EOL

class C
  def a_method
    'C#a_method'
  end
end

class D < C
end

obj = D.new
puts obj.a_method # => "C#a_method"





puts <<-EOL

1. superclass of singleton class

EOL

obj = D.new
class << obj
  def a_singleton_method
    'obj#a_singleton_method'
  end
end

puts obj.a_singleton_method # => "obj#a_singleton_method"
puts obj.singleton_class.superclass # => D




puts <<-EOL

3. singleton class

EOL

class C
  class << self # self is C
    def a_class_method # a.k.a) a_singleton_method
      'C.a_class_method'
    end
  end
end

puts C.a_class_method  # => "C.a_class_method"
puts C.singleton_class # => #<Class:C>
puts D.singleton_class # => #<Class:D>
puts D.singleton_class.superclass # => #<Class:C>
puts C.singleton_class.superclass # => #<Class:Object>
puts D.singleton_class.ancestors