title: C++ error: decomposition declaration not permitted in this context
body: <p>Why is <code>g++</code> giving an error like this?</p>
  
  <pre><code>blahblah.h:80:10: error: decomposition declaration not permitted in this context
  float[NUM_OUTPUTS] output_buffer;
  </code></pre>
  
  <p>(Already solved, but creating this because there's no good google hits for this error text, and the error message is inscrutable.)</p>