Class methods in Ruby on Rails 3 — I'm totally lost!

Question

Background here.

In the above link, the following example is given:

class << self
  def by_author(author)
    where(:author_id => author.id)
  end         


        

Answer 1

The following two bits of code are equivalent.

Using self.method:

class Hello
  def self.world
    puts "Hello, World!"
  end
end

Using class << self:

class Hello
  class << self
    def world
      puts "Hello, World!"
    end
  end
end

The only difference is readability, as well as the ease in refactoring. The class << self technique is often used when metaprogramming.

There is another thread that explains this. class << self vs self.method with Ruby: what's better?