title: Single or double slash when using PHP namespace?
body: <p>Both the following lines of calling name spaced method work, are there any case which single slash does not work?</p>
  
  <pre><code>&lt;?php
  
  namespace Foo\Bar;
  
  class Dummy {
      public static function hello() {
          echo 'world';
      }
  }
  
  echo \Foo\Bar\Dummy::hello();
  
  call_user_func('\Foo\Bar\Dummy::hello');
  call_user_func('\\Foo\\Bar\\Dummy::hello'); 
  </code></pre>
  
  <p>The reason I ask is: If single slash always work, why I see so many of double slash in the Internet, even the composer generate file like this [1]? Are there any case I am missing?</p>
  
  <p>[1] <a href="https://github.com/ircmaxell/quality-checker/blob/master/vendor/composer/autoload_namespaces.php" rel="noreferrer">https://github.com/ircmaxell/quality-checker/blob/master/vendor/composer/autoload_namespaces.php</a></p>