title: Ambiguous use of "??"
body: <p>I have a couple of lines of working code:</p>
  
  <pre><code>    let email = User.sharedInstance.emailAddress ?? ""
      accountEmailAddress.text = email
  </code></pre>
  
  <p><code>User.sharedInstance</code> is a non-optional instance of the <code>User</code> class. Its <code>emailAddress</code> property is an optional <code>String?</code>. <code>accountEmailAddress</code> is a UILabel.</p>
  
  <p>If I try to turn this into a single line of code:</p>
  
  <pre><code>    accountEmailAddress.text = User.sharedInstance.emailAddress ?? ""
  </code></pre>
  
  <p>I get the Swift compiler error "Ambiguous use of '??'".</p>
  
  <p>I can't quite figure out what's ambiguous about the use of the nil coalescing operator here. I'm looking to find out why the compiler's complaining, and, out of curiosity, if there's a way of making this a clean one-liner.</p>
  
  <p>(Xcode 6 beta 6.)</p>
  
  <p>Edit: Minimal reproduction in a playground:</p>
  
  <pre><code>// Playground - noun: a place where people can play
  var foo: String?
  var test: String?
  
  // "Ambiguous use of '??'"
  foo = test ?? "ValueIfNil"
  </code></pre>