Private attr methods in Ruby

You’re probably well aware that you can use the attr_ family of methods to create getters and setters for class attributes. You may not know that you can actually make these private without having to write your own.

Here’s a simple class with one attribute to demonstrate.

class Post

  def initialize
    @title = 'Default'

  attr_reader :title

  def rename!
    self.title = 'Renamed!'


  attr_writer :title


Here, the API allows @title to be read via the title instance method, created by attr_reader :title.

>> p.title
=> "Default"

However, @title may not be written to by the user of the Post class.

>> p.title = 'A New Title'
NoMethodError: private method `title=' called for #<Post:0x007fa8e8c3a378 @title="Default">
	from (irb):20
	from /Users/gareth/.rvm/rubies/ruby-1.9.3-p327/bin/irb:16:in `<main>'

You can still use #title= inside the Post class as you’d expect though.

>> p.rename!
=> "Renamed!"
>> p.title
=> "Renamed!"