title: Dynamically change aspect ratio of view controlled by autolayout
body: <h2>Problem</h2>
  
  <p>In UI I have some view which content is stretchable but should conserve some aspect ratio. This aspect ratio changes during run-time and views layout should be updated when some property describing aspect ratio changes.</p>
  
  <p>I've exposed <code>NSLayoutConstraint</code>, but its property used for aspect ratio: <code>multiplier</code> is read only. What is more funny similar property <code>constant</code> can be changed.</p>
  
  <h2>Possible solutions</h2>
  
  <ol>
  <li>I could just use constraint which fixes width or height and calculate it based on expected ratio, but this requires extra boiler plate code which will react on geometry/layout changes and I prefer to avoid this.</li>
  <li>I could experiment with <code>intrisicContentSize</code> and <code>sizeThatFits:</code> but I'm not sure how this should be used with <code>NSLayoutConstraint</code></li>
  </ol>