CODEWITHSUNDEEP
ruby-on-railsruby
PrivateUser
PrivateUser

Reputation: 4524

How to define a private method in Ruby?

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?

Upvotes: 10

Views: 6529

Answers (4)

Inversion
Inversion

Reputation: 1240

In Ruby 2.1 you can mark single methods as private also like this (space is optional):

class MyClass

    private \
    def private_method
        'private'
    end

    private\
    def private_method2
        'private2'
    end

    def public_method
        p private_method
        'public'
    end
end

t = MyClass.new
puts t.public_method        # will work
puts t.private_method       # Error: private method `private_method' 
                            #  called for #<MyClass:0x2d57228> (NoMethodError)

Upvotes: 2

Sirupsen
Sirupsen

Reputation: 2115

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

Upvotes: 9

nzifnab
nzifnab

Reputation: 16092

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 :)

Upvotes: 13

bjhaid
bjhaid

Reputation: 9762

It applies to everything under private i.e greeting and farewell

To make either of them private you can make greeting alone private as below:

def greeting
  random_response :greeting
end
private :greeting

def farewell
  radnom_response :farewell
end

Documentation is available at Module#private

Upvotes: 3

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