title: Use of module 'CALayer' as a type
body: <p>I want to port ITSwitch from obj-c to swift. <a href="https://github.com/iluuu1994/ITSwitch.git">https://github.com/iluuu1994/ITSwitch.git</a></p>
  
  <p>in ITSwitch.m</p>
  
  <pre><code>@property (readonly, strong) CALayer *rootLayer;
  </code></pre>
  
  <p>so in swift I write:</p>
  
  <pre><code>var rootLayer:CALayer?
  </code></pre>
  
  <p>but code give me this error:</p>
  
  <pre><code>Use of module 'CALayer' as a type
  </code></pre>
  
  <p>What's the error mean?
  How can I solve this?</p>