title: "FOUNDATION_EXPORT" vs "extern"
body: <p>I would like to ask what's the reason behind using <code>FOUNDATION_EXPORT</code> instead of <code>extern</code> in <em>Objective C</em> projects.</p>
  
  <p>I've checked <a href="https://stackoverflow.com/questions/538996/constants-in-objective-c">this question</a> and using <code>FOUNDATION_EXPORT</code> has earned whopping 340 points (1st place) whereas using <code>extern</code> only 74 points (2nd place). </p>
  
  <p>Could anybody explain why? Is there any practical reason for using <code>FOUNDATION_EXPORT</code> instead of <code>extern</code>?</p>
  
  <p>Thanks!</p>