title: Hiding access to a parent's property in the subclass
body: <p>I feel like this should be relatively simple but I can't find a way to accomplish it.</p>
  
  <p>Let say I have</p>
  
  <pre><code>class Parent {
     public var file: PFFile?
  }
  </code></pre>
  
  <p>and a subclass</p>
  
  <pre><code>class Child : Parent {
      // some functionality that hides access to super.file
  }
  </code></pre>
  
  <p>Problem is <strong>I can't mess with the Parent class</strong>, but I don't want anyone using the Child class to have access to 'file'. How can I accomplish this in Swift?</p>