title: Rails 4 attr_accessor doesn't work across multiple methods
body: <p>My model looks like this:</p>
  
  <pre><code>class Job &lt; ActiveRecord::Base
    attr_accessor :start_time
  
    def start_time
      self.start_time = Time.now
    end
  
    def elapsed_time
      end_time = Time.now
      elapsed = end_time - self.start_time
    end
  
  end
  </code></pre>
  
  <p>I want to measure the elapsed time, and <code>self.start_time</code> exists within the <code>start_time</code> method. However, in my <code>elapsed_time</code> method, <code>self.start_time</code> is nil. Why is that?</p>
  
  <p>I am using rails 4.1.0 and ruby 2.0.0.</p>