title: Replacing a swift String with another string at a specific index
body: <p>Lets say I have a Swift string </p>
  
  <blockquote>
    <p>"Hello I'm John Doe"</p>
  </blockquote>
  
  <p>I want to replace John Doe with:</p>
  
  <blockquote>
    <p>Steve.</p>
  </blockquote>
  
  <p>How is that done with Swift 3?  The syntax is taking me forever to figure out.  </p>
  
  <p>I've tried a few things, one of them is x.replaceSubrange, but it has a syntax that I'm not able to figure out.</p>
  
  <blockquote>
    <p>x?.replaceSubrange(&lt;#T##bounds: Range##Range#>, with: &lt;#T##String#>)</p>
  </blockquote>
  
  <p>I tried to create a range with NSRange, but it didn't like that either.  </p>