title: merge vector into existing vector
body: <p>In C++, given <code>vector&lt;T&gt; src, dst</code>, both already sorted, is there a <em>more efficient</em> way to merge the contents of <code>src</code> into <code>dst</code> than</p>
  
  <pre><code>size_t n = dst.size();
  dst.insert(dst.end(), src.begin(), src.end());
  std::inplace_merge(dst.begin(), dst.begin() + n, dst.end());
  </code></pre>
  
  <p>?  In the case I care about, <code>T</code> is a small (12-16 bytes, depending on ABI) POD structure, but each vector contains millions of elements, so the total amount of memory in play is tens to hundreds of megabytes.</p>