title: Add atomic<double> and double
body: <p>I want to add two values:</p>
  
  <pre><code>auto size = new std::atomic&lt;double&gt;(0);
  double packet_size = 64e3;
  *size += packet_size;
  </code></pre>
  
  <p>But I got an error.</p>
  
  <pre><code>no match for ‘operator+=’ (operand types are ‘std::atomic&lt;double&gt;’ and ‘double’)
  </code></pre>
  
  <p>How should I correctly add these two numbers?</p>