title: Update the constant property of a constraint programmatically in Swift?
body: <p>I want to animate an object, so I declare a constraint and add it to the view. I then update the <code>constant</code> property of the constraint inside an <code>UIView</code> animation. Why doesn't this code move the object?</p>
  
  <pre><code>UIView.animateWithDuration(1, animations: {
       myConstraint.constant = 0   
       self.view.updateConstraints(myConstraint)
  })
  </code></pre>