title: Empty Class in Swift Playground Gives __lldb_expr_ Error
body: <p>Knocking up an empty class within a Swift Playground gives an error <strong>__lldb_expr_</strong></p>
  
  <pre><code>//: Playground - noun: a place where people can play
  
  import UIKit
  
  class FooBar {
  
  }
  
  let foo = FooBar()
  </code></pre>
  
  <p>See attached screenshot. 
  <img src="https://i.stack.imgur.com/iJRHA.png" alt="__lldb_expr_4 at line 12 on attempted instantiation of class FooBar"></p>
  
  <p>This occurs on Xcode Version <strong>6.3.1 (6D1002)</strong>. I have also tried with the latest Xcode 6.4 beta 3 - <strong>Version 6.4 (6E7)</strong> - available 11th May 2015. The same error occurs.</p>
  
  <p>Empty classes build without issue in a normal Swift project.</p>
  
  <p>The error can be avoided by simply adding a dummy constant as follows:</p>
  
  <pre><code>//: Playground - noun: a place where people can play
  
  import UIKit
  
  class FooBar {
      let wibble = 10
  }
  
  let foo = FooBar()
  </code></pre>
  
  <p>Was surprised at this error given that creating a initial empty class is such a basic thing. In my case I wanted a scroll view delegate class to track content offsets. It would seem entirely reasonable to use a delegate with no properties. </p>
  
  <p>Any ideas?</p>