title: simple structs with make_unique and emplace_back
body: <p>Given a struct:</p>
  
  <pre><code>struct S {
      int x;
      int y;
  }
  </code></pre>
  
  <p>Why the Standard allows us to do this:</p>
  
  <pre><code>std::vector&lt;S&gt; vec;
  vec.emplace_back(1, 2);
  </code></pre>
  
  <p>But does not allow to do this:</p>
  
  <pre><code>auto ptr = std::make_unique&lt;S&gt;(1, 2);
  </code></pre>
  
  <p>?</p>