title: Swift property - getter ivar
body: <p>Is there an ivar property we should use in a Swift getter? My code is causing the getter to call the getter until the program crashes:</p>
  
  <pre><code>var document: UIDocument? {
      get {
          return self.document
      }
      set {
          self.document = newValue
  
          useDocument()
      }
  }
  </code></pre>