title: IActionResult misunderstanding
body: <p>I just downloaded <strong>music store</strong> (microsoft sample projct) source code that based on ASP.NET 5. I don't understand there why developers from Microsoft use IActionResult interface as a return type in controllers. </p>
  
  <p><strong>What is a reason of IActionResult interface usage?</strong> Why don't just use ActionResult type.</p>
  
  <p><a href="https://i.stack.imgur.com/qnRet.png" rel="noreferrer"><img src="https://i.stack.imgur.com/qnRet.png" alt="enter image description here"></a></p>