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3 ways to make class methods private in Ruby

An overview of the different ways to make class methods private in Ruby

In this article we’re going to explore the following topics:

• private_class_method
• class << self and private

private_class_method

This method takes one or more method_ids as an argument. A method_id can be either a String or a Symbol that represents an existing class method in the context of self. The private_class_method makes the method correspond to the method_id passed as argument private

Here we can see that by passing :hello as argument of private_class_method the A::hello class method becomes private.

Now let’s see another way to make class methods private by also using private_class_method

Here private_class_method takes the hello class method definition as an argument. Then we can see that our hello class method is private.

To understand what happens here, let’s slightly modify our code

Here we store the return value of the hello class method definition in method_id. Then we pass method_id (which contains :hello) to private_class_method. At this moment, the hello class method becomes private.

So as a method definition returns the method identifier, we can directly pass the method definition as an argument of private_class_method.

class << self and private

The classic way to make class methods private is to open the eigenclass and use the private keyword on the instance methods of the eigenclass — which is what you commonly refer to as class methods.

Feel free to have a quick look to my article about the eigenclass if you’re not familiar with this concept.

Here, we simply open the eigenclass and make the hello class method private.

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