title: Swift Struct: adding new parameters at runtime
body: <p>Given an instance of struct like this: </p>
  
  <pre><code>struct Size {
      var width: Int
      var height: Int
  }
  </code></pre>
  
  <p>Is there the possibility to extend it by runtime to: </p>
  
  <pre><code>struct Size {
      var width: Int
      var height: Int
      var depth: Int
  }
  </code></pre>
  
  <p>adding a new parameter to the existing instance of Size struct ? </p>
  
  <p>Thanks</p>