title: The standard way to get sizeof(promoted(x))
body: <p>Is there a standard way to get the size of the type a variable would be promoted to when passed as a variadic argument?</p>
  
  <pre><code>auto x = ...;
  auto y = sizeof(promoted(x));
  </code></pre>
  
  <p>The results should be:</p>
  
  <pre><code>char  -&gt; sizeof(int)
  int   -&gt; sizeof(int)
  float -&gt; sizeof(double)
  ...
  </code></pre>