# 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

```ruby
obj = Object.new

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

obj.my_singleton_method('Hello')
```

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1715906794461/b11307b4-a7c8-4d78-a3bb-3b01e4ef56fe.png align="center")

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

```ruby
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')
```

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1715906882334/35f94abb-5f9f-49ea-9f07-65b5ad1d971c.png align="center")

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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