title: Swift "Extraneous argument label in 'contentsOf' in call" when trying to use insert on a String
body: <p>I'm working in a swift playground while going through the Swift documentation on Apple's website. Specifically <a href="https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html#//apple_ref/doc/uid/TP40014097-CH7-ID285" rel="nofollow noreferrer">here.</a> First I have to say it is pretty challenging because several of the methods they describe are not current and have different syntax than in the documentation. I've found the answers to all my questions up to now in previous questions that have been asked on here. This one I can't seem to find exactly. Anyways I have resorted to directly copy pasting the code from the documentation and it still isn't working. Here it is:</p>
  
  <pre><code>import UIKit
  var welcome = "hello"
  welcome.insert(contentsOf: " there", at: welcome.index(before: welcome.endIndex))
  </code></pre>
  
  <p>And I am told that contentsOf is extraneous. Swift even suggested this exact method as I typed it in, argument labels and all. Any insight is much appreciated. </p>
  
  <p>Edit: Thanks folks, answered. </p>