title: How to convert NSURLRequest to NSMutableURLRequest in Swift 3?
body: <p>I'm in the process of migrating one of my projects to Swift 3 and I'm hung up on converting a NSURLRequest to NSURLMutableRequest. In Swift 2 I could simply:</p>
  
  <pre><code>let mreq = req.mutableCopy() as! NSMutableURLRequest
  </code></pre>
  
  <p>But now mutableCopy is no longer a thing in Swift 3. I tried various permutations of constructors and looked in the docs for info to no avail. I must be missing something. There has to be a way to make a mutable copy of an object. </p>