title: class << self vs self.method with Ruby: what's better?
body: <p>This <a href="https://github.com/styleguide/ruby" rel="noreferrer">Ruby Style Guide</a> tells that is better using <code>self.method_name</code> instead of <code>class method_name</code>. But Why?</p>
  
  <pre><code>class TestClass
    # bad
    class &lt;&lt; self
      def first_method
        # body omitted
      end
  
      def second_method_etc
        # body omitted
      end
    end
  
    # good
    def self.first_method
      # body omitted
    end
  
    def self.second_method_etc
      # body omitted
    end
  end
  </code></pre>
  
  <p>Are there performance issues?</p>