title: Swift .uppercaseString or .lowercaseString property replacement
body: <p>Since Strings in Swift no longer have the .uppercaseString or .lowercaseString properties available, how would i go about performing that function?</p>
  
  <p>If i have for example:</p>
  
  <pre><code>var sillyString = "This is a string!"
  let yellyString = sillyString.uppercaseString
  let silentString = sillyString.lowercaseString
  </code></pre>
  
  <p>I would like to take sillyString and mutate it into either uppercase or lowercase. How would i go about doing that now?</p>
  
  <p>Thanks in advance!</p>