title: std::initializer_list variations
body: <p>What are the differences between the following three initializations with <code>std::initializer_list</code>s?</p>
  
  <pre><code>std::vector&lt;int&gt; a{ 2, 3, 5, 7};
  std::vector&lt;int&gt; b( { 2, 3, 5, 7} );
  std::vector&lt;int&gt; c = { 2, 3, 5, 7};
  </code></pre>
  
  <p>In the above example, <code>std::vector</code> is just a placeholder, but I am interested in a general answer.</p>