Ruby Singleton methods for class and objects

Question

I am learning Ruby Singletons and i found some ways to define and get list of Class and Object singleton methods.

Class Singleton Methods

Ways to define

Answer 1

Some more ways:

Class singleton methods

class << MyClass
  define_method :sixth_sing_method do
    puts "sixth"
  end
end

class MyClass
  class << self
    define_method :fourth_sing_method do
      puts "seventh"
    end
  end
end

Object singleton methods

class << obj
  define_method :fourth_sing_method do
    puts "fourth"
  end
end

Next, you can use define_method and define_singleton_method in combination with send, e.g.

obj.send :define_singleton_method, :nth_sing_method, lambda{ puts "nth" }

and all possible combinations thereof. To use define_method, you need to capture the singleton class first as in this (the same works for class objects, too)

singleton_class = class << obj; self end
singleton_class.send :define_method, :nth_sing_method, lambda{ puts "nth" }

Another ways is using class_eval on the singleton class objects:

singleton_class.class_eval do
  def nth_sing_method
    puts "nth"
  end
end

And then you once again may combine send with class_eval...

There are myriads of ways, I guess :)