title: @IBInspectable NSLayoutConstraint doesn't work Xcode 8.2.1 (8C1002)
body: <p>I have a strange behaviour, constraints do not want to be updated in Interface Builder.</p>
  
  <p>Here are 2 variants of my code and both don't work.</p>
  
  <pre><code>extension NSLayoutConstraint {
  
      @IBInspectable var preciseConstant: CGFloat {
          get {
              return constant * UIScreen.main.scale
          }
          set {
              constant = CGFloat(newValue) / UIScreen.main.scale
          }
      }
  }
  
  @IBDesignable class CustomLayoutConstraint: NSLayoutConstraint {
      @IBInspectable var screenHeight: CGFloat = 0.0 {
          didSet {
              changeContraint()
          }
      }
  
      func changeContraint() {
          self.constant = self.screenHeight / UIScreen.main.scale
      }
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/bWOv4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bWOv4.jpg" alt="enter image description here"></a></p>
  
  <p>Is there  my mistake or it's bug Xcode? </p>