title: Computed property generates "Overriding declaration requires an 'override' keyword" error
body: <p>Code below. Why does the "Overriding declaration requires an 'override' keyword" error occur? Isn't this the "Swift" way of providing getters and setters to properties?</p>
  
  <pre><code>class TestClass : UICollectionViewCell {
          var _selected = false
  
          var selected : Bool {
          get {
              return _selected
          }
  
          set {
              _selected = newValue
              selectedView.hidden = !_selected
          }
      }
  }
  </code></pre>