Singleton class. Singleton method Vs Class method.

Every object is associated with two classes. One is which we can get using class method of object(eg: "hello".class) and the other is called the eigenclass(or singleton class).

The singleton methods of an object are the instance methods of the anonymous eigenclass associated with that object.

To open up an singleton class of an object str, use class << str

Eg:

	str = "hello world"
	class << str #open singleton class
	def m1
	puts "singleton method m1 of object str"
	end
	end
	str.singleton_class.instance_methods.include?(:m1) # =>true

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 Thus, singleton class is an anonymous class associated with every object.


A method added to a single object rather than to a class of objects is known as singleton method. Also the class methods on a class are nothing more than singleton methods on the Class instance that represent that class.

Eg:

	class Foo
	end
	f = Foo.new
	def f.print_smth #singleton method
	puts "hello world"
	end
	f.print_smth # => hello world
	f1 = Foo.new
	f1.print_smth # error : undefined method

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On the other hand, class methods are invoked only through the constant refering to the Class object.

Eg:

	class Bar # Bar is Class instance
	def self.hello # class method created using self. Also singleton method of Bar
	puts "hello"
	end
	def Bar.world # class method created using class name. Also singleton method of Bar
	puts "world"
	end
	end
	Bar.hello # => hello
	Bar.world # => world

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