title: Create typescript interface as union of other interfaces
body: <p>I have a list of interfaces that extends one basic interface.</p>
  
  <p>I have also some functions that can accept any of these interfaces.</p>
  
  <p>I would like to create a new interface that describe that kind of parameter.</p>
  
  <p>So I have something like this:</p>
  
  <pre><code>interface BasicInterface {...};
  
  interface A extends BasicInterface {...};
  interface B extends BasicInterface {...};
  </code></pre>
  
  <p>and I would like something like </p>
  
  <pre><code>interface C = A | B;
  </code></pre>
  
  <p>I know in my functions I can do </p>
  
  <pre><code>function X(param1: A | B) {};
  </code></pre>
  
  <p>but since it is more than one function I would like to have just one interface for all of them</p>