How to list the attr_accessor class?

Question

Ruby on Rails

Help me to understand in detail the following implementation of the code found on the internet:

class MyBaseClass
  def self.attr_accessor(*vars)
    @attributes ||= []
    @attributes.concat vars
    super(*vars)
  end

  def self.attributes
    @attributes
  end

  def attributes
    self.class.attributes
  end
end

class SubClass < MyBaseClass
  attr_accessor :id, :title, :body
end

SubClass.new.attributes.inspect #=> [:id, :title, :body]

This line is especially interesting @attributes ||= []

Answer 1

About the operator ||=: assignment occurs if the variable is empty.