title: Swift 3 incorrect string interpolation with implicitly unwrapped Optionals
body: <p>Why are <strong>implicitly unwrapped optionals</strong> not unwrapped when using string interpolation in Swift 3?</p>
  
  <p><strong>Example</strong>:
  Running the following code in the playground</p>
  
  <pre><code>var str: String!
  str = "Hello"
  
  print("The following should not be printed as an optional: \(str)")
  </code></pre>
  
  <p>produces this output: </p>
  
  <pre><code>The following should not be printed as an optional: Optional("Hello")
  </code></pre>
  
  <p>Of course I can concatenate strings with the <code>+</code> operator but I'm using string interpolation pretty much everywhere in my app which now doesn't work anymore due to this (bug?). </p>
  
  <p>Is this even a bug or did they intentionally change this behaviour with Swift 3?</p>