title: Why would I ever use push_back instead of emplace_back?
body: <p>C++11 vectors have the new function <code>emplace_back</code>. Unlike <code>push_back</code>, which relies on compiler optimizations to avoid copies, <code>emplace_back</code> uses perfect forwarding to send the arguments directly to the constructor to create an object in-place. It seems to me that <code>emplace_back</code> does everything <code>push_back</code> can do, but some of the time it will do it better (but never worse).</p>
  
  <p>What reason do I have to use <code>push_back</code>?</p>