Singleton Methods in Ruby

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Singleton method

Definition

A singleton method, in the context of object-oriented programming, is a method that is defined for a single instance (or object) of a class rather than for the class as a whole.

It's called "singleton" because it belongs to a single instance of the class, rather than being shared among all instances.

A singleton method is a method that is defined for a single object rather than a class. This means that the method is only available to that particular object and not to other instances of the same class.

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Ruby

As we said, a singleton method belongs to a specific instance of a class, rather than being shared among all instances.

In order to implement a singleton method in Ruby, it's necessary to use the object's name, followed by .(dot) and choose a method name.

It'll look something like obj.method_name.

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Implementation

obj = Object.new

def obj.my_singleton_method(value)
  puts "#{value} comes from the singleton method in #{self}"
end

obj.my_singleton_method('Hello')

In the previous example, the my_singleton_method is defined only for the obj instance, and it won't be available for other instances of the same class.

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Unavailable for other instances

obj = Object.new
obj2 = Object.new

def obj.my_singleton_method(value)
  puts "#{value} comes from the singleton method in #{self}"
end

obj.my_singleton_method('Hello')
obj2.my_singleton_method('Hello')

In case you try to use my_singleton_method on a another object, you'll get an undefined method.

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Done

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Conclusion

By following these steps, you can easily visualize how singleton methods work in Ruby.

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