title: How can we put a variant message ( one of a few message types ) inside a protobuf message?
body: <p>How can we put a variant message ( one of a few message types ) inside a protobuf message?</p>
  
  <pre><code>message typeA {
      ....
  }
  
  message typeB {
      ....
  }
  
  message typeC {
      [typeB|typeA] payload;
  }
  </code></pre>