title: Meaning of double bracket "[[foo()]] type name;" syntax in c++?
body: <p>In <a href="http://www.drdobbs.com/parallel/eliminate-false-sharing/217500206?pgno=4" rel="noreferrer">this</a> article about avoiding False Sharing, the following code snipped for alignment is presented:</p>
  
  <pre><code>// C++ (using C++0x alignment syntax)
  template&lt;typename T&gt;
  struct cache_line_storage {
     [[ align(CACHE_LINE_SIZE) ]] T data;
     char pad[ CACHE_LINE_SIZE &gt; sizeof(T)
          ? CACHE_LINE_SIZE - sizeof(T)
          : 1 ];
  };
  </code></pre>
  
  <p>What is the meaning of line 4?
  I've never seen this double bracket syntax before.</p>