title: Class variables lifetime in ruby
body: <p>I have a class variable named fields which is initiated like this:</p>
  
  <pre><code>@@fields ||= JSON.parse(@client.run_request(@request_path, 'get', params))["data"]
  </code></pre>
  
  <p>after the first time the method is called, in another rails request, <code>@@fields</code> still holds the </p>
  
  <p>When does this value expire?</p>