title: Swift 3: String search backwards
body: <p>I want to search backwards in a string. But all examples I found are not running on current Swift 3.0. ".BackwardsSearch" is not an option available on my XCode 8. Any idea, how this can be done?
  Example:</p>
  
  <pre><code>let rPos = rIndex(sourceString, searchString)
  </code></pre>
  
  <p>or </p>
  
  <pre><code>let rPos = sourceString.rindex(of: searchString)
  </code></pre>