title: Why are there no custom default values in proto3?
body: <p>The <strong>proto2</strong> version of Protocol Buffers allows to specify default values for message elements:</p>
  
  <pre><code>optional double scaling_factor = 3 [default = 1.0];
  </code></pre>
  
  <p>Why is this no longer possible in <strong>proto3</strong>? I consider this a neat feature to save additional bytes on the wire without the need of writing any wrapper code.</p>