How to define a private method in Ruby?

Question

Just started to learn Ruby. I'm confused with Ruby's private keyword.

Let's say I have code like this

private

def greeting
  random_response :greeting
end

def farewell
  random_response :farewell
end

Does private only applied to the #greeting or both - #greeting and #farewell?

Answer 1

It's fairly standard to put private/protected methods at the bottom of the file. Everything after private will become a private method.

class MyClass

  def a_public_method

  end

  private

    def a_private_method
    end

    def another_private_method
    end

  protected
    def a_protected_method
    end

  public
    def another_public_method
    end
end

As you can see in this example, if you really need to you can go back to declaring public methods by using the public keyword.

It can also be easier to see where the scope changes by indenting your private/public methods another level, to see visually that they are grouped under the private section etc.

You also have the option to only declare one-off private methods like this:

class MyClass

  def a_public_method

  end

  def a_private_method
  end

  def another_private_method
  end
  private :a_private_method, :another_private_method
end

Using the private module method to declare only single methods as private, but frankly unless you're always doing it right after each method declaration it can be a bit confusing that way to find the private methods. I just prefer to stick them at the bottom :)

Answer 2

In Ruby 2.1 method definitions return their name, so you can call private on the class passing the function definition. You can also pass the method name to private. Anything defined after private without any arguments will be a private method.

This leaves you with three different methods of declaring a private method:

class MyClass
  def public_method
  end

  private def private_method
  end

  def other_private_method
  end
  private :other_private_method

  private
  def third_private_method
  end
end