title: Emplacing a std::pair
body: <p>Is there a way of emplacing a <code>std::pair</code>?</p>
  
  <pre><code>std::unordered_map&lt;int, std::pair&lt;std::string, std::string&gt;&gt; my_map;
  my_map.emplace(1, "foo", "bar"); // Error
  </code></pre>
  
  <p>Of course inserting is possible:</p>
  
  <pre><code>my_map[2] = std::make_pair("bar", "foo");
  </code></pre>
  
  <p>But doesn't this require unnecessary copying/moving?</p>