title: Circle UIView resize with animation keeping Circle shape
body: <p>I have a UIView which I am making the background a circular shape with:</p>
  
  <pre><code> self.colourView.layer.cornerRadius = 350
   self.colourView.clipsToBounds = true
  </code></pre>
  
  <p>With the view being a 700 by 700 square.</p>
  
  <p>I am then trying to change the size of this view using:</p>
  
  <pre><code>UIView.animate(withDuration: zoomLength,
                                     delay: 0,
                                     options: .curveEaseIn,
                                     animations: {
                                      self.colorViewWidth.constant = 100
                                      self.colorViewHeight.constant = 100
  
                                      self.colourView.layer.cornerRadius = 50
                                      self.colourView.clipsToBounds = true
                                      self.view.layoutIfNeeded()
                                      },
                                     completion: { finished in
  
                                          })
  
                                      })
  </code></pre>
  
  <p>The problem with this is the corner radius of the view switch to 50 instantly. So that as the view shrinks in size it doesn't look like a circle shrinking but a square with rounded corners until it reaches the 100 by 100 size.</p>
  
  <p>How can I take a view that circule in shape and shrink it down while maintaining the circlare shape during the animation.</p>