title: Can protobuf service method return primitive type?
body: <p>I'm trying to use Google protobuf and i 'm having the next descriptions:</p>
  <p><strong>message.proto</strong> file:</p>
  <pre><code>message Request {
     required int32 id = 1;
     optional string value = 2;
  }
  </code></pre>
  <p><strong>service.proto</strong> file:</p>
  <pre><code>import &quot;message.proto&quot;;
  
  service Service {
      rpc request (Request) returns (bool);
  }
  </code></pre>
  <p>I'm trying to generate c++ sources and getting an error:</p>
  <blockquote>
  <p>$ protoc service.proto --cpp_out=/tmp/proto/build</p>
  <p>service.proto:4:40: Expected message type.</p>
  </blockquote>
  <p>Do i have to return user-defined types only? Are primitive (like <code>bool</code> or <code>string</code>) supported?  Can i use primitive types as service method argument (instead of <code>Request</code> in my example)?</p>