title: How to build Swift 3 project on Xcode 9?
body: <p><a href="https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/WhatsNewXcode/xcode_9/xcode_9.html" rel="noreferrer">Xcode 9 Release Notes</a> says that Swift 3 compilation is supported:</p>
  
  <blockquote>
    <p><strong>One compiler for Swift 4 and Swift 3</strong>, Swift 4 and Swift 3 targets can be compiled together in the same project.</p>
  </blockquote>
  
  <p>I have installed Xcode 9 beta.
  But when I press Build it shows bunch of errors. Are some special preparations need to do when use Swift 3 in Xcode 9?</p>
  
  <p>UPD:
  <img src="https://i.stack.imgur.com/in0Ks.png" alt="Module compiled with Swift 3.1 cannot be imported in Swift 4.0"></p>
  
  <p>Module compiled with Swift 3.1 cannot be imported in Swift 4.0</p>